Refactor routing in App component to enhance navigation and improve error handling by integrating dynamic routes and updating the NotFound route.

node_modules/micromark-extension-gfm-footnote/dev/index.d.ts

@@ -0,0 +1,164 @@
+export {gfmFootnoteHtml, defaultBackLabel} from './lib/html.js'
+export {gfmFootnote} from './lib/syntax.js'
+
+/**
+ * Generate a back label dynamically.
+ *
+ * For the following markdown:
+ *
+ * ```markdown
+ * Alpha[^micromark], bravo[^micromark], and charlie[^remark].
+ *
+ * [^remark]: things about remark
+ * [^micromark]: things about micromark
+ * ```
+ *
+ * This function will be called with:
+ *
+ * * `0` and `0` for the backreference from `things about micromark` to
+ *  `alpha`, as it is the first used definition, and the first call to it
+ * * `0` and `1` for the backreference from `things about micromark` to
+ *  `bravo`, as it is the first used definition, and the second call to it
+ * * `1` and `0` for the backreference from `things about remark` to
+ *  `charlie`, as it is the second used definition
+ *
+ * @param referenceIndex
+ *   Index of the definition in the order that they are first referenced,
+ *   0-indexed.
+ * @param rereferenceIndex
+ *   Index of calls to the same definition, 0-indexed.
+ * @returns
+ *   Back label to use when linking back from definitions to their reference.
+ */
+export type BackLabelTemplate = (
+  referenceIndex: number,
+  rereferenceIndex: number
+) => string
+
+/**
+ * Configuration.
+ */
+export interface HtmlOptions {
+  /**
+   * Prefix to use before the `id` attribute on footnotes to prevent them from
+   * *clobbering* (default: `'user-content-'`).
+   *
+   * Pass `''` for trusted markdown and when you are careful with
+   * polyfilling.
+   * You could pass a different prefix.
+   *
+   * DOM clobbering is this:
+   *
+   * ```html
+   * <p id="x"></p>
+   * <script>alert(x) // `x` now refers to the `p#x` DOM element</script>
+   * ```
+   *
+   * The above example shows that elements are made available by browsers, by
+   * their ID, on the `window` object.
+   * This is a security risk because you might be expecting some other variable
+   * at that place.
+   * It can also break polyfills.
+   * Using a prefix solves these problems.
+   */
+  clobberPrefix?: string | null | undefined
+  /**
+   * Textual label to use for the footnotes section (default: `'Footnotes'`).
+   *
+   * Change it when the markdown is not in English.
+   *
+   * This label is typically hidden visually (assuming a `sr-only` CSS class
+   * is defined that does that) and so affects screen readers only.
+   * If you do have such a class, but want to show this section to everyone,
+   * pass different attributes with the `labelAttributes` option.
+   */
+  label?: string | null | undefined
+  /**
+   * Attributes to use on the footnote label (default: `'class="sr-only"'`).
+   *
+   * Change it to show the label and add other attributes.
+   *
+   * This label is typically hidden visually (assuming an `sr-only` CSS class
+   * is defined that does that) and so affects screen readers only.
+   * If you do have such a class, but want to show this section to everyone,
+   * pass an empty string.
+   * You can also add different attributes.
+   *
+   * > 👉 **Note**: `id="footnote-label"` is always added, because footnote
+   * > calls use it with `aria-describedby` to provide an accessible label.
+   */
+  labelAttributes?: string | null | undefined
+  /**
+   * HTML tag name to use for the footnote label element (default: `'h2'`).
+   *
+   * Change it to match your document structure.
+   *
+   * This label is typically hidden visually (assuming a `sr-only` CSS class
+   * is defined that does that) and so affects screen readers only.
+   * If you do have such a class, but want to show this section to everyone,
+   * pass different attributes with the `labelAttributes` option.
+   */
+  labelTagName?: string | null | undefined
+  /**
+   * Textual label to describe the backreference back to references (default:
+   * `defaultBackLabel`).
+   *
+   * The default value is:
+   *
+   * ```js
+   * function defaultBackLabel(referenceIndex, rereferenceIndex) {
+   *   return (
+   *     'Back to reference ' +
+   *     (referenceIndex + 1) +
+   *     (rereferenceIndex > 1 ? '-' + rereferenceIndex : '')
+   *   )
+   * }
+   * ```
+   *
+   * Change it when the markdown is not in English.
+   *
+   * This label is used in the `aria-label` attribute on each backreference
+   * (the `↩` links).
+   * It affects users of assistive technology.
+   */
+  backLabel?: BackLabelTemplate | string | null | undefined
+}
+
+/**
+ * Augment types.
+ */
+declare module 'micromark-util-types' {
+  /**
+   * Compile data.
+   */
+  interface CompileData {
+    gfmFootnoteDefinitions?: Record<string, string>
+    gfmFootnoteDefinitionStack?: Array<string>
+    gfmFootnoteCallCounts?: Record<string, number>
+    gfmFootnoteCallOrder?: Array<string>
+  }
+
+  /**
+   * Parse context.
+   */
+  interface ParseContext {
+    gfmFootnotes?: Array<string>
+  }
+
+  /**
+   * Token types.
+   */
+  interface TokenTypeMap {
+    gfmFootnoteCall: 'gfmFootnoteCall'
+    gfmFootnoteCallLabelMarker: 'gfmFootnoteCallLabelMarker'
+    gfmFootnoteCallMarker: 'gfmFootnoteCallMarker'
+    gfmFootnoteCallString: 'gfmFootnoteCallString'
+    gfmFootnoteDefinition: 'gfmFootnoteDefinition'
+    gfmFootnoteDefinitionIndent: 'gfmFootnoteDefinitionIndent'
+    gfmFootnoteDefinitionLabel: 'gfmFootnoteDefinitionLabel'
+    gfmFootnoteDefinitionLabelMarker: 'gfmFootnoteDefinitionLabelMarker'
+    gfmFootnoteDefinitionLabelString: 'gfmFootnoteDefinitionLabelString'
+    gfmFootnoteDefinitionMarker: 'gfmFootnoteDefinitionMarker'
+    gfmFootnoteDefinitionWhitespace: 'gfmFootnoteDefinitionWhitespace'
+  }
+}

node_modules/micromark-extension-gfm-footnote/dev/index.js

@@ -0,0 +1,3 @@
+// Note: types are exported from `dev/index.d.ts`.
+export {gfmFootnote} from './lib/syntax.js'
+export {gfmFootnoteHtml, defaultBackLabel} from './lib/html.js'

node_modules/micromark-extension-gfm-footnote/dev/lib/html.d.ts

@@ -0,0 +1,25 @@
+/**
+ * Generate the default label that GitHub uses on backreferences.
+ *
+ * @param {number} referenceIndex
+ *   Index of the definition in the order that they are first referenced,
+ *   0-indexed.
+ * @param {number} rereferenceIndex
+ *   Index of calls to the same definition, 0-indexed.
+ * @returns {string}
+ *   Default label.
+ */
+export function defaultBackLabel(referenceIndex: number, rereferenceIndex: number): string;
+/**
+ * Create an extension for `micromark` to support GFM footnotes when
+ * serializing to HTML.
+ *
+ * @param {Options | null | undefined} [options={}]
+ *   Configuration (optional).
+ * @returns {HtmlExtension}
+ *   Extension for `micromark` that can be passed in `htmlExtensions` to
+ *   support GFM footnotes when serializing to HTML.
+ */
+export function gfmFootnoteHtml(options?: Options | null | undefined): HtmlExtension;
+import type { HtmlOptions as Options } from 'micromark-extension-gfm-footnote';
+import type { HtmlExtension } from 'micromark-util-types';

node_modules/micromark-extension-gfm-footnote/dev/lib/html.js

@@ -0,0 +1,226 @@
+/**
+ * @import {HtmlOptions as Options} from 'micromark-extension-gfm-footnote'
+ * @import {HtmlExtension} from 'micromark-util-types'
+ */
+
+import {ok as assert} from 'devlop'
+import {normalizeIdentifier} from 'micromark-util-normalize-identifier'
+import {sanitizeUri} from 'micromark-util-sanitize-uri'
+
+const own = {}.hasOwnProperty
+
+/** @type {Options} */
+const emptyOptions = {}
+
+/**
+ * Generate the default label that GitHub uses on backreferences.
+ *
+ * @param {number} referenceIndex
+ *   Index of the definition in the order that they are first referenced,
+ *   0-indexed.
+ * @param {number} rereferenceIndex
+ *   Index of calls to the same definition, 0-indexed.
+ * @returns {string}
+ *   Default label.
+ */
+export function defaultBackLabel(referenceIndex, rereferenceIndex) {
+  return (
+    'Back to reference ' +
+    (referenceIndex + 1) +
+    (rereferenceIndex > 1 ? '-' + rereferenceIndex : '')
+  )
+}
+
+/**
+ * Create an extension for `micromark` to support GFM footnotes when
+ * serializing to HTML.
+ *
+ * @param {Options | null | undefined} [options={}]
+ *   Configuration (optional).
+ * @returns {HtmlExtension}
+ *   Extension for `micromark` that can be passed in `htmlExtensions` to
+ *   support GFM footnotes when serializing to HTML.
+ */
+export function gfmFootnoteHtml(options) {
+  const config = options || emptyOptions
+  const label = config.label || 'Footnotes'
+  const labelTagName = config.labelTagName || 'h2'
+  const labelAttributes =
+    config.labelAttributes === null || config.labelAttributes === undefined
+      ? 'class="sr-only"'
+      : config.labelAttributes
+  const backLabel = config.backLabel || defaultBackLabel
+  const clobberPrefix =
+    config.clobberPrefix === null || config.clobberPrefix === undefined
+      ? 'user-content-'
+      : config.clobberPrefix
+  return {
+    enter: {
+      gfmFootnoteDefinition() {
+        const stack = this.getData('tightStack')
+        stack.push(false)
+      },
+      gfmFootnoteDefinitionLabelString() {
+        this.buffer()
+      },
+      gfmFootnoteCallString() {
+        this.buffer()
+      }
+    },
+    exit: {
+      gfmFootnoteDefinition() {
+        let definitions = this.getData('gfmFootnoteDefinitions')
+        const footnoteStack = this.getData('gfmFootnoteDefinitionStack')
+        assert(footnoteStack, 'expected `footnoteStack`')
+        const tightStack = this.getData('tightStack')
+        const current = footnoteStack.pop()
+        const value = this.resume()
+
+        assert(current, 'expected to be in a footnote')
+
+        if (!definitions) {
+          this.setData('gfmFootnoteDefinitions', (definitions = {}))
+        }
+
+        if (!own.call(definitions, current)) definitions[current] = value
+
+        tightStack.pop()
+        this.setData('slurpOneLineEnding', true)
+        // “Hack” to prevent a line ending from showing up if we’re in a definition in
+        // an empty list item.
+        this.setData('lastWasTag')
+      },
+      gfmFootnoteDefinitionLabelString(token) {
+        let footnoteStack = this.getData('gfmFootnoteDefinitionStack')
+
+        if (!footnoteStack) {
+          this.setData('gfmFootnoteDefinitionStack', (footnoteStack = []))
+        }
+
+        footnoteStack.push(normalizeIdentifier(this.sliceSerialize(token)))
+        this.resume() // Drop the label.
+        this.buffer() // Get ready for a value.
+      },
+      gfmFootnoteCallString(token) {
+        let calls = this.getData('gfmFootnoteCallOrder')
+        let counts = this.getData('gfmFootnoteCallCounts')
+        const id = normalizeIdentifier(this.sliceSerialize(token))
+        /** @type {number} */
+        let counter
+
+        this.resume()
+
+        if (!calls) this.setData('gfmFootnoteCallOrder', (calls = []))
+        if (!counts) this.setData('gfmFootnoteCallCounts', (counts = {}))
+
+        const index = calls.indexOf(id)
+        const safeId = sanitizeUri(id.toLowerCase())
+
+        if (index === -1) {
+          calls.push(id)
+          counts[id] = 1
+          counter = calls.length
+        } else {
+          counts[id]++
+          counter = index + 1
+        }
+
+        const reuseCounter = counts[id]
+
+        this.tag(
+          '<sup><a href="#' +
+            clobberPrefix +
+            'fn-' +
+            safeId +
+            '" id="' +
+            clobberPrefix +
+            'fnref-' +
+            safeId +
+            (reuseCounter > 1 ? '-' + reuseCounter : '') +
+            '" data-footnote-ref="" aria-describedby="footnote-label">' +
+            String(counter) +
+            '</a></sup>'
+        )
+      },
+      null() {
+        const calls = this.getData('gfmFootnoteCallOrder') || []
+        const counts = this.getData('gfmFootnoteCallCounts') || {}
+        const definitions = this.getData('gfmFootnoteDefinitions') || {}
+        let index = -1
+
+        if (calls.length > 0) {
+          this.lineEndingIfNeeded()
+          this.tag(
+            '<section data-footnotes="" class="footnotes"><' +
+              labelTagName +
+              ' id="footnote-label"' +
+              (labelAttributes ? ' ' + labelAttributes : '') +
+              '>'
+          )
+          this.raw(this.encode(label))
+          this.tag('</' + labelTagName + '>')
+          this.lineEndingIfNeeded()
+          this.tag('<ol>')
+        }
+
+        while (++index < calls.length) {
+          // Called definitions are always defined.
+          const id = calls[index]
+          const safeId = sanitizeUri(id.toLowerCase())
+          let referenceIndex = 0
+          /** @type {Array<string>} */
+          const references = []
+
+          while (++referenceIndex <= counts[id]) {
+            references.push(
+              '<a href="#' +
+                clobberPrefix +
+                'fnref-' +
+                safeId +
+                (referenceIndex > 1 ? '-' + referenceIndex : '') +
+                '" data-footnote-backref="" aria-label="' +
+                this.encode(
+                  typeof backLabel === 'string'
+                    ? backLabel
+                    : backLabel(index, referenceIndex)
+                ) +
+                '" class="data-footnote-backref">↩' +
+                (referenceIndex > 1
+                  ? '<sup>' + referenceIndex + '</sup>'
+                  : '') +
+                '</a>'
+            )
+          }
+
+          const reference = references.join(' ')
+          let injected = false
+
+          this.lineEndingIfNeeded()
+          this.tag('<li id="' + clobberPrefix + 'fn-' + safeId + '">')
+          this.lineEndingIfNeeded()
+          this.tag(
+            definitions[id].replace(/<\/p>(?:\r?\n|\r)?$/, function ($0) {
+              injected = true
+              return ' ' + reference + $0
+            })
+          )
+
+          if (!injected) {
+            this.lineEndingIfNeeded()
+            this.tag(reference)
+          }
+
+          this.lineEndingIfNeeded()
+          this.tag('</li>')
+        }
+
+        if (calls.length > 0) {
+          this.lineEndingIfNeeded()
+          this.tag('</ol>')
+          this.lineEndingIfNeeded()
+          this.tag('</section>')
+        }
+      }
+    }
+  }
+}

node_modules/micromark-extension-gfm-footnote/dev/lib/syntax.d.ts

@@ -0,0 +1,9 @@
+/**
+ * Create an extension for `micromark` to enable GFM footnote syntax.
+ *
+ * @returns {Extension}
+ *   Extension for `micromark` that can be passed in `extensions` to
+ *   enable GFM footnote syntax.
+ */
+export function gfmFootnote(): Extension;
+import type { Extension } from 'micromark-util-types';

node_modules/micromark-extension-gfm-footnote/dev/lib/syntax.js

@@ -0,0 +1,558 @@
+/**
+ * @import {Event, Exiter, Extension, Resolver, State, Token, TokenizeContext, Tokenizer} from 'micromark-util-types'
+ */
+
+import {ok as assert} from 'devlop'
+import {blankLine} from 'micromark-core-commonmark'
+import {factorySpace} from 'micromark-factory-space'
+import {markdownLineEndingOrSpace} from 'micromark-util-character'
+import {normalizeIdentifier} from 'micromark-util-normalize-identifier'
+import {codes, constants, types} from 'micromark-util-symbol'
+
+const indent = {tokenize: tokenizeIndent, partial: true}
+
+// To do: micromark should support a `_hiddenGfmFootnoteSupport`, which only
+// affects label start (image).
+// That will let us drop `tokenizePotentialGfmFootnote*`.
+// It currently has a `_hiddenFootnoteSupport`, which affects that and more.
+// That can be removed when `micromark-extension-footnote` is archived.
+
+/**
+ * Create an extension for `micromark` to enable GFM footnote syntax.
+ *
+ * @returns {Extension}
+ *   Extension for `micromark` that can be passed in `extensions` to
+ *   enable GFM footnote syntax.
+ */
+export function gfmFootnote() {
+  /** @type {Extension} */
+  return {
+    document: {
+      [codes.leftSquareBracket]: {
+        name: 'gfmFootnoteDefinition',
+        tokenize: tokenizeDefinitionStart,
+        continuation: {tokenize: tokenizeDefinitionContinuation},
+        exit: gfmFootnoteDefinitionEnd
+      }
+    },
+    text: {
+      [codes.leftSquareBracket]: {
+        name: 'gfmFootnoteCall',
+        tokenize: tokenizeGfmFootnoteCall
+      },
+      [codes.rightSquareBracket]: {
+        name: 'gfmPotentialFootnoteCall',
+        add: 'after',
+        tokenize: tokenizePotentialGfmFootnoteCall,
+        resolveTo: resolveToPotentialGfmFootnoteCall
+      }
+    }
+  }
+}
+
+// To do: remove after micromark update.
+/**
+ * @this {TokenizeContext}
+ * @type {Tokenizer}
+ */
+function tokenizePotentialGfmFootnoteCall(effects, ok, nok) {
+  const self = this
+  let index = self.events.length
+  const defined = self.parser.gfmFootnotes || (self.parser.gfmFootnotes = [])
+  /** @type {Token} */
+  let labelStart
+
+  // Find an opening.
+  while (index--) {
+    const token = self.events[index][1]
+
+    if (token.type === types.labelImage) {
+      labelStart = token
+      break
+    }
+
+    // Exit if we’ve walked far enough.
+    if (
+      token.type === 'gfmFootnoteCall' ||
+      token.type === types.labelLink ||
+      token.type === types.label ||
+      token.type === types.image ||
+      token.type === types.link
+    ) {
+      break
+    }
+  }
+
+  return start
+
+  /**
+   * @type {State}
+   */
+  function start(code) {
+    assert(code === codes.rightSquareBracket, 'expected `]`')
+
+    if (!labelStart || !labelStart._balanced) {
+      return nok(code)
+    }
+
+    const id = normalizeIdentifier(
+      self.sliceSerialize({start: labelStart.end, end: self.now()})
+    )
+
+    if (id.codePointAt(0) !== codes.caret || !defined.includes(id.slice(1))) {
+      return nok(code)
+    }
+
+    effects.enter('gfmFootnoteCallLabelMarker')
+    effects.consume(code)
+    effects.exit('gfmFootnoteCallLabelMarker')
+    return ok(code)
+  }
+}
+
+// To do: remove after micromark update.
+/** @type {Resolver} */
+function resolveToPotentialGfmFootnoteCall(events, context) {
+  let index = events.length
+  /** @type {Token | undefined} */
+  let labelStart
+
+  // Find an opening.
+  while (index--) {
+    if (
+      events[index][1].type === types.labelImage &&
+      events[index][0] === 'enter'
+    ) {
+      labelStart = events[index][1]
+      break
+    }
+  }
+
+  assert(labelStart, 'expected `labelStart` to resolve')
+
+  // Change the `labelImageMarker` to a `data`.
+  events[index + 1][1].type = types.data
+  events[index + 3][1].type = 'gfmFootnoteCallLabelMarker'
+
+  // The whole (without `!`):
+  /** @type {Token} */
+  const call = {
+    type: 'gfmFootnoteCall',
+    start: Object.assign({}, events[index + 3][1].start),
+    end: Object.assign({}, events[events.length - 1][1].end)
+  }
+  // The `^` marker
+  /** @type {Token} */
+  const marker = {
+    type: 'gfmFootnoteCallMarker',
+    start: Object.assign({}, events[index + 3][1].end),
+    end: Object.assign({}, events[index + 3][1].end)
+  }
+  // Increment the end 1 character.
+  marker.end.column++
+  marker.end.offset++
+  marker.end._bufferIndex++
+  /** @type {Token} */
+  const string = {
+    type: 'gfmFootnoteCallString',
+    start: Object.assign({}, marker.end),
+    end: Object.assign({}, events[events.length - 1][1].start)
+  }
+  /** @type {Token} */
+  const chunk = {
+    type: types.chunkString,
+    contentType: 'string',
+    start: Object.assign({}, string.start),
+    end: Object.assign({}, string.end)
+  }
+
+  /** @type {Array<Event>} */
+  const replacement = [
+    // Take the `labelImageMarker` (now `data`, the `!`)
+    events[index + 1],
+    events[index + 2],
+    ['enter', call, context],
+    // The `[`
+    events[index + 3],
+    events[index + 4],
+    // The `^`.
+    ['enter', marker, context],
+    ['exit', marker, context],
+    // Everything in between.
+    ['enter', string, context],
+    ['enter', chunk, context],
+    ['exit', chunk, context],
+    ['exit', string, context],
+    // The ending (`]`, properly parsed and labelled).
+    events[events.length - 2],
+    events[events.length - 1],
+    ['exit', call, context]
+  ]
+
+  events.splice(index, events.length - index + 1, ...replacement)
+
+  return events
+}
+
+/**
+ * @this {TokenizeContext}
+ * @type {Tokenizer}
+ */
+function tokenizeGfmFootnoteCall(effects, ok, nok) {
+  const self = this
+  const defined = self.parser.gfmFootnotes || (self.parser.gfmFootnotes = [])
+  let size = 0
+  /** @type {boolean} */
+  let data
+
+  // Note: the implementation of `markdown-rs` is different, because it houses
+  // core *and* extensions in one project.
+  // Therefore, it can include footnote logic inside `label-end`.
+  // We can’t do that, but luckily, we can parse footnotes in a simpler way than
+  // needed for labels.
+  return start
+
+  /**
+   * Start of footnote label.
+   *
+   * ```markdown
+   * > | a [^b] c
+   *       ^
+   * ```
+   *
+   * @type {State}
+   */
+  function start(code) {
+    assert(code === codes.leftSquareBracket, 'expected `[`')
+    effects.enter('gfmFootnoteCall')
+    effects.enter('gfmFootnoteCallLabelMarker')
+    effects.consume(code)
+    effects.exit('gfmFootnoteCallLabelMarker')
+    return callStart
+  }
+
+  /**
+   * After `[`, at `^`.
+   *
+   * ```markdown
+   * > | a [^b] c
+   *        ^
+   * ```
+   *
+   * @type {State}
+   */
+  function callStart(code) {
+    if (code !== codes.caret) return nok(code)
+
+    effects.enter('gfmFootnoteCallMarker')
+    effects.consume(code)
+    effects.exit('gfmFootnoteCallMarker')
+    effects.enter('gfmFootnoteCallString')
+    effects.enter('chunkString').contentType = 'string'
+    return callData
+  }
+
+  /**
+   * In label.
+   *
+   * ```markdown
+   * > | a [^b] c
+   *         ^
+   * ```
+   *
+   * @type {State}
+   */
+  function callData(code) {
+    if (
+      // Too long.
+      size > constants.linkReferenceSizeMax ||
+      // Closing brace with nothing.
+      (code === codes.rightSquareBracket && !data) ||
+      // Space or tab is not supported by GFM for some reason.
+      // `\n` and `[` not being supported makes sense.
+      code === codes.eof ||
+      code === codes.leftSquareBracket ||
+      markdownLineEndingOrSpace(code)
+    ) {
+      return nok(code)
+    }
+
+    if (code === codes.rightSquareBracket) {
+      effects.exit('chunkString')
+      const token = effects.exit('gfmFootnoteCallString')
+
+      if (!defined.includes(normalizeIdentifier(self.sliceSerialize(token)))) {
+        return nok(code)
+      }
+
+      effects.enter('gfmFootnoteCallLabelMarker')
+      effects.consume(code)
+      effects.exit('gfmFootnoteCallLabelMarker')
+      effects.exit('gfmFootnoteCall')
+      return ok
+    }
+
+    if (!markdownLineEndingOrSpace(code)) {
+      data = true
+    }
+
+    size++
+    effects.consume(code)
+    return code === codes.backslash ? callEscape : callData
+  }
+
+  /**
+   * On character after escape.
+   *
+   * ```markdown
+   * > | a [^b\c] d
+   *           ^
+   * ```
+   *
+   * @type {State}
+   */
+  function callEscape(code) {
+    if (
+      code === codes.leftSquareBracket ||
+      code === codes.backslash ||
+      code === codes.rightSquareBracket
+    ) {
+      effects.consume(code)
+      size++
+      return callData
+    }
+
+    return callData(code)
+  }
+}
+
+/**
+ * @this {TokenizeContext}
+ * @type {Tokenizer}
+ */
+function tokenizeDefinitionStart(effects, ok, nok) {
+  const self = this
+  const defined = self.parser.gfmFootnotes || (self.parser.gfmFootnotes = [])
+  /** @type {string} */
+  let identifier
+  let size = 0
+  /** @type {boolean | undefined} */
+  let data
+
+  return start
+
+  /**
+   * Start of GFM footnote definition.
+   *
+   * ```markdown
+   * > | [^a]: b
+   *     ^
+   * ```
+   *
+   * @type {State}
+   */
+  function start(code) {
+    assert(code === codes.leftSquareBracket, 'expected `[`')
+    effects.enter('gfmFootnoteDefinition')._container = true
+    effects.enter('gfmFootnoteDefinitionLabel')
+    effects.enter('gfmFootnoteDefinitionLabelMarker')
+    effects.consume(code)
+    effects.exit('gfmFootnoteDefinitionLabelMarker')
+    return labelAtMarker
+  }
+
+  /**
+   * In label, at caret.
+   *
+   * ```markdown
+   * > | [^a]: b
+   *      ^
+   * ```
+   *
+   * @type {State}
+   */
+  function labelAtMarker(code) {
+    if (code === codes.caret) {
+      effects.enter('gfmFootnoteDefinitionMarker')
+      effects.consume(code)
+      effects.exit('gfmFootnoteDefinitionMarker')
+      effects.enter('gfmFootnoteDefinitionLabelString')
+      effects.enter('chunkString').contentType = 'string'
+      return labelInside
+    }
+
+    return nok(code)
+  }
+
+  /**
+   * In label.
+   *
+   * > 👉 **Note**: `cmark-gfm` prevents whitespace from occurring in footnote
+   * > definition labels.
+   *
+   * ```markdown
+   * > | [^a]: b
+   *       ^
+   * ```
+   *
+   * @type {State}
+   */
+  function labelInside(code) {
+    if (
+      // Too long.
+      size > constants.linkReferenceSizeMax ||
+      // Closing brace with nothing.
+      (code === codes.rightSquareBracket && !data) ||
+      // Space or tab is not supported by GFM for some reason.
+      // `\n` and `[` not being supported makes sense.
+      code === codes.eof ||
+      code === codes.leftSquareBracket ||
+      markdownLineEndingOrSpace(code)
+    ) {
+      return nok(code)
+    }
+
+    if (code === codes.rightSquareBracket) {
+      effects.exit('chunkString')
+      const token = effects.exit('gfmFootnoteDefinitionLabelString')
+      identifier = normalizeIdentifier(self.sliceSerialize(token))
+      effects.enter('gfmFootnoteDefinitionLabelMarker')
+      effects.consume(code)
+      effects.exit('gfmFootnoteDefinitionLabelMarker')
+      effects.exit('gfmFootnoteDefinitionLabel')
+      return labelAfter
+    }
+
+    if (!markdownLineEndingOrSpace(code)) {
+      data = true
+    }
+
+    size++
+    effects.consume(code)
+    return code === codes.backslash ? labelEscape : labelInside
+  }
+
+  /**
+   * After `\`, at a special character.
+   *
+   * > 👉 **Note**: `cmark-gfm` currently does not support escaped brackets:
+   * > <https://github.com/github/cmark-gfm/issues/240>
+   *
+   * ```markdown
+   * > | [^a\*b]: c
+   *         ^
+   * ```
+   *
+   * @type {State}
+   */
+  function labelEscape(code) {
+    if (
+      code === codes.leftSquareBracket ||
+      code === codes.backslash ||
+      code === codes.rightSquareBracket
+    ) {
+      effects.consume(code)
+      size++
+      return labelInside
+    }
+
+    return labelInside(code)
+  }
+
+  /**
+   * After definition label.
+   *
+   * ```markdown
+   * > | [^a]: b
+   *         ^
+   * ```
+   *
+   * @type {State}
+   */
+  function labelAfter(code) {
+    if (code === codes.colon) {
+      effects.enter('definitionMarker')
+      effects.consume(code)
+      effects.exit('definitionMarker')
+
+      if (!defined.includes(identifier)) {
+        defined.push(identifier)
+      }
+
+      // Any whitespace after the marker is eaten, forming indented code
+      // is not possible.
+      // No space is also fine, just like a block quote marker.
+      return factorySpace(
+        effects,
+        whitespaceAfter,
+        'gfmFootnoteDefinitionWhitespace'
+      )
+    }
+
+    return nok(code)
+  }
+
+  /**
+   * After definition prefix.
+   *
+   * ```markdown
+   * > | [^a]: b
+   *           ^
+   * ```
+   *
+   * @type {State}
+   */
+  function whitespaceAfter(code) {
+    // `markdown-rs` has a wrapping token for the prefix that is closed here.
+    return ok(code)
+  }
+}
+
+/**
+ * @this {TokenizeContext}
+ * @type {Tokenizer}
+ */
+function tokenizeDefinitionContinuation(effects, ok, nok) {
+  /// Start of footnote definition continuation.
+  ///
+  /// ```markdown
+  ///   | [^a]: b
+  /// > |     c
+  ///     ^
+  /// ```
+  //
+  // Either a blank line, which is okay, or an indented thing.
+  return effects.check(blankLine, ok, effects.attempt(indent, ok, nok))
+}
+
+/** @type {Exiter} */
+function gfmFootnoteDefinitionEnd(effects) {
+  effects.exit('gfmFootnoteDefinition')
+}
+
+/**
+ * @this {TokenizeContext}
+ * @type {Tokenizer}
+ */
+function tokenizeIndent(effects, ok, nok) {
+  const self = this
+
+  return factorySpace(
+    effects,
+    afterPrefix,
+    'gfmFootnoteDefinitionIndent',
+    constants.tabSize + 1
+  )
+
+  /**
+   * @type {State}
+   */
+  function afterPrefix(code) {
+    const tail = self.events[self.events.length - 1]
+    return tail &&
+      tail[1].type === 'gfmFootnoteDefinitionIndent' &&
+      tail[2].sliceSerialize(tail[1], true).length === constants.tabSize
+      ? ok(code)
+      : nok(code)
+  }
+}

node_modules/micromark-extension-gfm-footnote/index.d.ts

@@ -0,0 +1,164 @@
+export {gfmFootnoteHtml, defaultBackLabel} from './lib/html.js'
+export {gfmFootnote} from './lib/syntax.js'
+
+/**
+ * Generate a back label dynamically.
+ *
+ * For the following markdown:
+ *
+ * ```markdown
+ * Alpha[^micromark], bravo[^micromark], and charlie[^remark].
+ *
+ * [^remark]: things about remark
+ * [^micromark]: things about micromark
+ * ```
+ *
+ * This function will be called with:
+ *
+ * * `0` and `0` for the backreference from `things about micromark` to
+ *  `alpha`, as it is the first used definition, and the first call to it
+ * * `0` and `1` for the backreference from `things about micromark` to
+ *  `bravo`, as it is the first used definition, and the second call to it
+ * * `1` and `0` for the backreference from `things about remark` to
+ *  `charlie`, as it is the second used definition
+ *
+ * @param referenceIndex
+ *   Index of the definition in the order that they are first referenced,
+ *   0-indexed.
+ * @param rereferenceIndex
+ *   Index of calls to the same definition, 0-indexed.
+ * @returns
+ *   Back label to use when linking back from definitions to their reference.
+ */
+export type BackLabelTemplate = (
+  referenceIndex: number,
+  rereferenceIndex: number
+) => string
+
+/**
+ * Configuration.
+ */
+export interface HtmlOptions {
+  /**
+   * Prefix to use before the `id` attribute on footnotes to prevent them from
+   * *clobbering* (default: `'user-content-'`).
+   *
+   * Pass `''` for trusted markdown and when you are careful with
+   * polyfilling.
+   * You could pass a different prefix.
+   *
+   * DOM clobbering is this:
+   *
+   * ```html
+   * <p id="x"></p>
+   * <script>alert(x) // `x` now refers to the `p#x` DOM element</script>
+   * ```
+   *
+   * The above example shows that elements are made available by browsers, by
+   * their ID, on the `window` object.
+   * This is a security risk because you might be expecting some other variable
+   * at that place.
+   * It can also break polyfills.
+   * Using a prefix solves these problems.
+   */
+  clobberPrefix?: string | null | undefined
+  /**
+   * Textual label to use for the footnotes section (default: `'Footnotes'`).
+   *
+   * Change it when the markdown is not in English.
+   *
+   * This label is typically hidden visually (assuming a `sr-only` CSS class
+   * is defined that does that) and so affects screen readers only.
+   * If you do have such a class, but want to show this section to everyone,
+   * pass different attributes with the `labelAttributes` option.
+   */
+  label?: string | null | undefined
+  /**
+   * Attributes to use on the footnote label (default: `'class="sr-only"'`).
+   *
+   * Change it to show the label and add other attributes.
+   *
+   * This label is typically hidden visually (assuming an `sr-only` CSS class
+   * is defined that does that) and so affects screen readers only.
+   * If you do have such a class, but want to show this section to everyone,
+   * pass an empty string.
+   * You can also add different attributes.
+   *
+   * > 👉 **Note**: `id="footnote-label"` is always added, because footnote
+   * > calls use it with `aria-describedby` to provide an accessible label.
+   */
+  labelAttributes?: string | null | undefined
+  /**
+   * HTML tag name to use for the footnote label element (default: `'h2'`).
+   *
+   * Change it to match your document structure.
+   *
+   * This label is typically hidden visually (assuming a `sr-only` CSS class
+   * is defined that does that) and so affects screen readers only.
+   * If you do have such a class, but want to show this section to everyone,
+   * pass different attributes with the `labelAttributes` option.
+   */
+  labelTagName?: string | null | undefined
+  /**
+   * Textual label to describe the backreference back to references (default:
+   * `defaultBackLabel`).
+   *
+   * The default value is:
+   *
+   * ```js
+   * function defaultBackLabel(referenceIndex, rereferenceIndex) {
+   *   return (
+   *     'Back to reference ' +
+   *     (referenceIndex + 1) +
+   *     (rereferenceIndex > 1 ? '-' + rereferenceIndex : '')
+   *   )
+   * }
+   * ```
+   *
+   * Change it when the markdown is not in English.
+   *
+   * This label is used in the `aria-label` attribute on each backreference
+   * (the `↩` links).
+   * It affects users of assistive technology.
+   */
+  backLabel?: BackLabelTemplate | string | null | undefined
+}
+
+/**
+ * Augment types.
+ */
+declare module 'micromark-util-types' {
+  /**
+   * Compile data.
+   */
+  interface CompileData {
+    gfmFootnoteDefinitions?: Record<string, string>
+    gfmFootnoteDefinitionStack?: Array<string>
+    gfmFootnoteCallCounts?: Record<string, number>
+    gfmFootnoteCallOrder?: Array<string>
+  }
+
+  /**
+   * Parse context.
+   */
+  interface ParseContext {
+    gfmFootnotes?: Array<string>
+  }
+
+  /**
+   * Token types.
+   */
+  interface TokenTypeMap {
+    gfmFootnoteCall: 'gfmFootnoteCall'
+    gfmFootnoteCallLabelMarker: 'gfmFootnoteCallLabelMarker'
+    gfmFootnoteCallMarker: 'gfmFootnoteCallMarker'
+    gfmFootnoteCallString: 'gfmFootnoteCallString'
+    gfmFootnoteDefinition: 'gfmFootnoteDefinition'
+    gfmFootnoteDefinitionIndent: 'gfmFootnoteDefinitionIndent'
+    gfmFootnoteDefinitionLabel: 'gfmFootnoteDefinitionLabel'
+    gfmFootnoteDefinitionLabelMarker: 'gfmFootnoteDefinitionLabelMarker'
+    gfmFootnoteDefinitionLabelString: 'gfmFootnoteDefinitionLabelString'
+    gfmFootnoteDefinitionMarker: 'gfmFootnoteDefinitionMarker'
+    gfmFootnoteDefinitionWhitespace: 'gfmFootnoteDefinitionWhitespace'
+  }
+}

node_modules/micromark-extension-gfm-footnote/index.js

@@ -0,0 +1,3 @@
+// Note: types are exported from `dev/index.d.ts`.
+export { gfmFootnote } from './lib/syntax.js';
+export { gfmFootnoteHtml, defaultBackLabel } from './lib/html.js';

node_modules/micromark-extension-gfm-footnote/lib/html.d.ts

@@ -0,0 +1,25 @@
+/**
+ * Generate the default label that GitHub uses on backreferences.
+ *
+ * @param {number} referenceIndex
+ *   Index of the definition in the order that they are first referenced,
+ *   0-indexed.
+ * @param {number} rereferenceIndex
+ *   Index of calls to the same definition, 0-indexed.
+ * @returns {string}
+ *   Default label.
+ */
+export function defaultBackLabel(referenceIndex: number, rereferenceIndex: number): string;
+/**
+ * Create an extension for `micromark` to support GFM footnotes when
+ * serializing to HTML.
+ *
+ * @param {Options | null | undefined} [options={}]
+ *   Configuration (optional).
+ * @returns {HtmlExtension}
+ *   Extension for `micromark` that can be passed in `htmlExtensions` to
+ *   support GFM footnotes when serializing to HTML.
+ */
+export function gfmFootnoteHtml(options?: Options | null | undefined): HtmlExtension;
+import type { HtmlOptions as Options } from 'micromark-extension-gfm-footnote';
+import type { HtmlExtension } from 'micromark-util-types';

node_modules/micromark-extension-gfm-footnote/lib/html.js

@@ -0,0 +1,154 @@
+/**
+ * @import {HtmlOptions as Options} from 'micromark-extension-gfm-footnote'
+ * @import {HtmlExtension} from 'micromark-util-types'
+ */
+
+import { normalizeIdentifier } from 'micromark-util-normalize-identifier';
+import { sanitizeUri } from 'micromark-util-sanitize-uri';
+const own = {}.hasOwnProperty;
+
+/** @type {Options} */
+const emptyOptions = {};
+
+/**
+ * Generate the default label that GitHub uses on backreferences.
+ *
+ * @param {number} referenceIndex
+ *   Index of the definition in the order that they are first referenced,
+ *   0-indexed.
+ * @param {number} rereferenceIndex
+ *   Index of calls to the same definition, 0-indexed.
+ * @returns {string}
+ *   Default label.
+ */
+export function defaultBackLabel(referenceIndex, rereferenceIndex) {
+  return 'Back to reference ' + (referenceIndex + 1) + (rereferenceIndex > 1 ? '-' + rereferenceIndex : '');
+}
+
+/**
+ * Create an extension for `micromark` to support GFM footnotes when
+ * serializing to HTML.
+ *
+ * @param {Options | null | undefined} [options={}]
+ *   Configuration (optional).
+ * @returns {HtmlExtension}
+ *   Extension for `micromark` that can be passed in `htmlExtensions` to
+ *   support GFM footnotes when serializing to HTML.
+ */
+export function gfmFootnoteHtml(options) {
+  const config = options || emptyOptions;
+  const label = config.label || 'Footnotes';
+  const labelTagName = config.labelTagName || 'h2';
+  const labelAttributes = config.labelAttributes === null || config.labelAttributes === undefined ? 'class="sr-only"' : config.labelAttributes;
+  const backLabel = config.backLabel || defaultBackLabel;
+  const clobberPrefix = config.clobberPrefix === null || config.clobberPrefix === undefined ? 'user-content-' : config.clobberPrefix;
+  return {
+    enter: {
+      gfmFootnoteDefinition() {
+        const stack = this.getData('tightStack');
+        stack.push(false);
+      },
+      gfmFootnoteDefinitionLabelString() {
+        this.buffer();
+      },
+      gfmFootnoteCallString() {
+        this.buffer();
+      }
+    },
+    exit: {
+      gfmFootnoteDefinition() {
+        let definitions = this.getData('gfmFootnoteDefinitions');
+        const footnoteStack = this.getData('gfmFootnoteDefinitionStack');
+        const tightStack = this.getData('tightStack');
+        const current = footnoteStack.pop();
+        const value = this.resume();
+        if (!definitions) {
+          this.setData('gfmFootnoteDefinitions', definitions = {});
+        }
+        if (!own.call(definitions, current)) definitions[current] = value;
+        tightStack.pop();
+        this.setData('slurpOneLineEnding', true);
+        // “Hack” to prevent a line ending from showing up if we’re in a definition in
+        // an empty list item.
+        this.setData('lastWasTag');
+      },
+      gfmFootnoteDefinitionLabelString(token) {
+        let footnoteStack = this.getData('gfmFootnoteDefinitionStack');
+        if (!footnoteStack) {
+          this.setData('gfmFootnoteDefinitionStack', footnoteStack = []);
+        }
+        footnoteStack.push(normalizeIdentifier(this.sliceSerialize(token)));
+        this.resume(); // Drop the label.
+        this.buffer(); // Get ready for a value.
+      },
+      gfmFootnoteCallString(token) {
+        let calls = this.getData('gfmFootnoteCallOrder');
+        let counts = this.getData('gfmFootnoteCallCounts');
+        const id = normalizeIdentifier(this.sliceSerialize(token));
+        /** @type {number} */
+        let counter;
+        this.resume();
+        if (!calls) this.setData('gfmFootnoteCallOrder', calls = []);
+        if (!counts) this.setData('gfmFootnoteCallCounts', counts = {});
+        const index = calls.indexOf(id);
+        const safeId = sanitizeUri(id.toLowerCase());
+        if (index === -1) {
+          calls.push(id);
+          counts[id] = 1;
+          counter = calls.length;
+        } else {
+          counts[id]++;
+          counter = index + 1;
+        }
+        const reuseCounter = counts[id];
+        this.tag('<sup><a href="#' + clobberPrefix + 'fn-' + safeId + '" id="' + clobberPrefix + 'fnref-' + safeId + (reuseCounter > 1 ? '-' + reuseCounter : '') + '" data-footnote-ref="" aria-describedby="footnote-label">' + String(counter) + '</a></sup>');
+      },
+      null() {
+        const calls = this.getData('gfmFootnoteCallOrder') || [];
+        const counts = this.getData('gfmFootnoteCallCounts') || {};
+        const definitions = this.getData('gfmFootnoteDefinitions') || {};
+        let index = -1;
+        if (calls.length > 0) {
+          this.lineEndingIfNeeded();
+          this.tag('<section data-footnotes="" class="footnotes"><' + labelTagName + ' id="footnote-label"' + (labelAttributes ? ' ' + labelAttributes : '') + '>');
+          this.raw(this.encode(label));
+          this.tag('</' + labelTagName + '>');
+          this.lineEndingIfNeeded();
+          this.tag('<ol>');
+        }
+        while (++index < calls.length) {
+          // Called definitions are always defined.
+          const id = calls[index];
+          const safeId = sanitizeUri(id.toLowerCase());
+          let referenceIndex = 0;
+          /** @type {Array<string>} */
+          const references = [];
+          while (++referenceIndex <= counts[id]) {
+            references.push('<a href="#' + clobberPrefix + 'fnref-' + safeId + (referenceIndex > 1 ? '-' + referenceIndex : '') + '" data-footnote-backref="" aria-label="' + this.encode(typeof backLabel === 'string' ? backLabel : backLabel(index, referenceIndex)) + '" class="data-footnote-backref">↩' + (referenceIndex > 1 ? '<sup>' + referenceIndex + '</sup>' : '') + '</a>');
+          }
+          const reference = references.join(' ');
+          let injected = false;
+          this.lineEndingIfNeeded();
+          this.tag('<li id="' + clobberPrefix + 'fn-' + safeId + '">');
+          this.lineEndingIfNeeded();
+          this.tag(definitions[id].replace(/<\/p>(?:\r?\n|\r)?$/, function ($0) {
+            injected = true;
+            return ' ' + reference + $0;
+          }));
+          if (!injected) {
+            this.lineEndingIfNeeded();
+            this.tag(reference);
+          }
+          this.lineEndingIfNeeded();
+          this.tag('</li>');
+        }
+        if (calls.length > 0) {
+          this.lineEndingIfNeeded();
+          this.tag('</ol>');
+          this.lineEndingIfNeeded();
+          this.tag('</section>');
+        }
+      }
+    }
+  };
+}

node_modules/micromark-extension-gfm-footnote/lib/syntax.d.ts

@@ -0,0 +1,9 @@
+/**
+ * Create an extension for `micromark` to enable GFM footnote syntax.
+ *
+ * @returns {Extension}
+ *   Extension for `micromark` that can be passed in `extensions` to
+ *   enable GFM footnote syntax.
+ */
+export function gfmFootnote(): Extension;
+import type { Extension } from 'micromark-util-types';

node_modules/micromark-extension-gfm-footnote/lib/syntax.js

@@ -0,0 +1,485 @@
+/**
+ * @import {Event, Exiter, Extension, Resolver, State, Token, TokenizeContext, Tokenizer} from 'micromark-util-types'
+ */
+
+import { blankLine } from 'micromark-core-commonmark';
+import { factorySpace } from 'micromark-factory-space';
+import { markdownLineEndingOrSpace } from 'micromark-util-character';
+import { normalizeIdentifier } from 'micromark-util-normalize-identifier';
+const indent = {
+  tokenize: tokenizeIndent,
+  partial: true
+};
+
+// To do: micromark should support a `_hiddenGfmFootnoteSupport`, which only
+// affects label start (image).
+// That will let us drop `tokenizePotentialGfmFootnote*`.
+// It currently has a `_hiddenFootnoteSupport`, which affects that and more.
+// That can be removed when `micromark-extension-footnote` is archived.
+
+/**
+ * Create an extension for `micromark` to enable GFM footnote syntax.
+ *
+ * @returns {Extension}
+ *   Extension for `micromark` that can be passed in `extensions` to
+ *   enable GFM footnote syntax.
+ */
+export function gfmFootnote() {
+  /** @type {Extension} */
+  return {
+    document: {
+      [91]: {
+        name: 'gfmFootnoteDefinition',
+        tokenize: tokenizeDefinitionStart,
+        continuation: {
+          tokenize: tokenizeDefinitionContinuation
+        },
+        exit: gfmFootnoteDefinitionEnd
+      }
+    },
+    text: {
+      [91]: {
+        name: 'gfmFootnoteCall',
+        tokenize: tokenizeGfmFootnoteCall
+      },
+      [93]: {
+        name: 'gfmPotentialFootnoteCall',
+        add: 'after',
+        tokenize: tokenizePotentialGfmFootnoteCall,
+        resolveTo: resolveToPotentialGfmFootnoteCall
+      }
+    }
+  };
+}
+
+// To do: remove after micromark update.
+/**
+ * @this {TokenizeContext}
+ * @type {Tokenizer}
+ */
+function tokenizePotentialGfmFootnoteCall(effects, ok, nok) {
+  const self = this;
+  let index = self.events.length;
+  const defined = self.parser.gfmFootnotes || (self.parser.gfmFootnotes = []);
+  /** @type {Token} */
+  let labelStart;
+
+  // Find an opening.
+  while (index--) {
+    const token = self.events[index][1];
+    if (token.type === "labelImage") {
+      labelStart = token;
+      break;
+    }
+
+    // Exit if we’ve walked far enough.
+    if (token.type === 'gfmFootnoteCall' || token.type === "labelLink" || token.type === "label" || token.type === "image" || token.type === "link") {
+      break;
+    }
+  }
+  return start;
+
+  /**
+   * @type {State}
+   */
+  function start(code) {
+    if (!labelStart || !labelStart._balanced) {
+      return nok(code);
+    }
+    const id = normalizeIdentifier(self.sliceSerialize({
+      start: labelStart.end,
+      end: self.now()
+    }));
+    if (id.codePointAt(0) !== 94 || !defined.includes(id.slice(1))) {
+      return nok(code);
+    }
+    effects.enter('gfmFootnoteCallLabelMarker');
+    effects.consume(code);
+    effects.exit('gfmFootnoteCallLabelMarker');
+    return ok(code);
+  }
+}
+
+// To do: remove after micromark update.
+/** @type {Resolver} */
+function resolveToPotentialGfmFootnoteCall(events, context) {
+  let index = events.length;
+  /** @type {Token | undefined} */
+  let labelStart;
+
+  // Find an opening.
+  while (index--) {
+    if (events[index][1].type === "labelImage" && events[index][0] === 'enter') {
+      labelStart = events[index][1];
+      break;
+    }
+  }
+  // Change the `labelImageMarker` to a `data`.
+  events[index + 1][1].type = "data";
+  events[index + 3][1].type = 'gfmFootnoteCallLabelMarker';
+
+  // The whole (without `!`):
+  /** @type {Token} */
+  const call = {
+    type: 'gfmFootnoteCall',
+    start: Object.assign({}, events[index + 3][1].start),
+    end: Object.assign({}, events[events.length - 1][1].end)
+  };
+  // The `^` marker
+  /** @type {Token} */
+  const marker = {
+    type: 'gfmFootnoteCallMarker',
+    start: Object.assign({}, events[index + 3][1].end),
+    end: Object.assign({}, events[index + 3][1].end)
+  };
+  // Increment the end 1 character.
+  marker.end.column++;
+  marker.end.offset++;
+  marker.end._bufferIndex++;
+  /** @type {Token} */
+  const string = {
+    type: 'gfmFootnoteCallString',
+    start: Object.assign({}, marker.end),
+    end: Object.assign({}, events[events.length - 1][1].start)
+  };
+  /** @type {Token} */
+  const chunk = {
+    type: "chunkString",
+    contentType: 'string',
+    start: Object.assign({}, string.start),
+    end: Object.assign({}, string.end)
+  };
+
+  /** @type {Array<Event>} */
+  const replacement = [
+  // Take the `labelImageMarker` (now `data`, the `!`)
+  events[index + 1], events[index + 2], ['enter', call, context],
+  // The `[`
+  events[index + 3], events[index + 4],
+  // The `^`.
+  ['enter', marker, context], ['exit', marker, context],
+  // Everything in between.
+  ['enter', string, context], ['enter', chunk, context], ['exit', chunk, context], ['exit', string, context],
+  // The ending (`]`, properly parsed and labelled).
+  events[events.length - 2], events[events.length - 1], ['exit', call, context]];
+  events.splice(index, events.length - index + 1, ...replacement);
+  return events;
+}
+
+/**
+ * @this {TokenizeContext}
+ * @type {Tokenizer}
+ */
+function tokenizeGfmFootnoteCall(effects, ok, nok) {
+  const self = this;
+  const defined = self.parser.gfmFootnotes || (self.parser.gfmFootnotes = []);
+  let size = 0;
+  /** @type {boolean} */
+  let data;
+
+  // Note: the implementation of `markdown-rs` is different, because it houses
+  // core *and* extensions in one project.
+  // Therefore, it can include footnote logic inside `label-end`.
+  // We can’t do that, but luckily, we can parse footnotes in a simpler way than
+  // needed for labels.
+  return start;
+
+  /**
+   * Start of footnote label.
+   *
+   * ```markdown
+   * > | a [^b] c
+   *       ^
+   * ```
+   *
+   * @type {State}
+   */
+  function start(code) {
+    effects.enter('gfmFootnoteCall');
+    effects.enter('gfmFootnoteCallLabelMarker');
+    effects.consume(code);
+    effects.exit('gfmFootnoteCallLabelMarker');
+    return callStart;
+  }
+
+  /**
+   * After `[`, at `^`.
+   *
+   * ```markdown
+   * > | a [^b] c
+   *        ^
+   * ```
+   *
+   * @type {State}
+   */
+  function callStart(code) {
+    if (code !== 94) return nok(code);
+    effects.enter('gfmFootnoteCallMarker');
+    effects.consume(code);
+    effects.exit('gfmFootnoteCallMarker');
+    effects.enter('gfmFootnoteCallString');
+    effects.enter('chunkString').contentType = 'string';
+    return callData;
+  }
+
+  /**
+   * In label.
+   *
+   * ```markdown
+   * > | a [^b] c
+   *         ^
+   * ```
+   *
+   * @type {State}
+   */
+  function callData(code) {
+    if (
+    // Too long.
+    size > 999 ||
+    // Closing brace with nothing.
+    code === 93 && !data ||
+    // Space or tab is not supported by GFM for some reason.
+    // `\n` and `[` not being supported makes sense.
+    code === null || code === 91 || markdownLineEndingOrSpace(code)) {
+      return nok(code);
+    }
+    if (code === 93) {
+      effects.exit('chunkString');
+      const token = effects.exit('gfmFootnoteCallString');
+      if (!defined.includes(normalizeIdentifier(self.sliceSerialize(token)))) {
+        return nok(code);
+      }
+      effects.enter('gfmFootnoteCallLabelMarker');
+      effects.consume(code);
+      effects.exit('gfmFootnoteCallLabelMarker');
+      effects.exit('gfmFootnoteCall');
+      return ok;
+    }
+    if (!markdownLineEndingOrSpace(code)) {
+      data = true;
+    }
+    size++;
+    effects.consume(code);
+    return code === 92 ? callEscape : callData;
+  }
+
+  /**
+   * On character after escape.
+   *
+   * ```markdown
+   * > | a [^b\c] d
+   *           ^
+   * ```
+   *
+   * @type {State}
+   */
+  function callEscape(code) {
+    if (code === 91 || code === 92 || code === 93) {
+      effects.consume(code);
+      size++;
+      return callData;
+    }
+    return callData(code);
+  }
+}
+
+/**
+ * @this {TokenizeContext}
+ * @type {Tokenizer}
+ */
+function tokenizeDefinitionStart(effects, ok, nok) {
+  const self = this;
+  const defined = self.parser.gfmFootnotes || (self.parser.gfmFootnotes = []);
+  /** @type {string} */
+  let identifier;
+  let size = 0;
+  /** @type {boolean | undefined} */
+  let data;
+  return start;
+
+  /**
+   * Start of GFM footnote definition.
+   *
+   * ```markdown
+   * > | [^a]: b
+   *     ^
+   * ```
+   *
+   * @type {State}
+   */
+  function start(code) {
+    effects.enter('gfmFootnoteDefinition')._container = true;
+    effects.enter('gfmFootnoteDefinitionLabel');
+    effects.enter('gfmFootnoteDefinitionLabelMarker');
+    effects.consume(code);
+    effects.exit('gfmFootnoteDefinitionLabelMarker');
+    return labelAtMarker;
+  }
+
+  /**
+   * In label, at caret.
+   *
+   * ```markdown
+   * > | [^a]: b
+   *      ^
+   * ```
+   *
+   * @type {State}
+   */
+  function labelAtMarker(code) {
+    if (code === 94) {
+      effects.enter('gfmFootnoteDefinitionMarker');
+      effects.consume(code);
+      effects.exit('gfmFootnoteDefinitionMarker');
+      effects.enter('gfmFootnoteDefinitionLabelString');
+      effects.enter('chunkString').contentType = 'string';
+      return labelInside;
+    }
+    return nok(code);
+  }
+
+  /**
+   * In label.
+   *
+   * > 👉 **Note**: `cmark-gfm` prevents whitespace from occurring in footnote
+   * > definition labels.
+   *
+   * ```markdown
+   * > | [^a]: b
+   *       ^
+   * ```
+   *
+   * @type {State}
+   */
+  function labelInside(code) {
+    if (
+    // Too long.
+    size > 999 ||
+    // Closing brace with nothing.
+    code === 93 && !data ||
+    // Space or tab is not supported by GFM for some reason.
+    // `\n` and `[` not being supported makes sense.
+    code === null || code === 91 || markdownLineEndingOrSpace(code)) {
+      return nok(code);
+    }
+    if (code === 93) {
+      effects.exit('chunkString');
+      const token = effects.exit('gfmFootnoteDefinitionLabelString');
+      identifier = normalizeIdentifier(self.sliceSerialize(token));
+      effects.enter('gfmFootnoteDefinitionLabelMarker');
+      effects.consume(code);
+      effects.exit('gfmFootnoteDefinitionLabelMarker');
+      effects.exit('gfmFootnoteDefinitionLabel');
+      return labelAfter;
+    }
+    if (!markdownLineEndingOrSpace(code)) {
+      data = true;
+    }
+    size++;
+    effects.consume(code);
+    return code === 92 ? labelEscape : labelInside;
+  }
+
+  /**
+   * After `\`, at a special character.
+   *
+   * > 👉 **Note**: `cmark-gfm` currently does not support escaped brackets:
+   * > <https://github.com/github/cmark-gfm/issues/240>
+   *
+   * ```markdown
+   * > | [^a\*b]: c
+   *         ^
+   * ```
+   *
+   * @type {State}
+   */
+  function labelEscape(code) {
+    if (code === 91 || code === 92 || code === 93) {
+      effects.consume(code);
+      size++;
+      return labelInside;
+    }
+    return labelInside(code);
+  }
+
+  /**
+   * After definition label.
+   *
+   * ```markdown
+   * > | [^a]: b
+   *         ^
+   * ```
+   *
+   * @type {State}
+   */
+  function labelAfter(code) {
+    if (code === 58) {
+      effects.enter('definitionMarker');
+      effects.consume(code);
+      effects.exit('definitionMarker');
+      if (!defined.includes(identifier)) {
+        defined.push(identifier);
+      }
+
+      // Any whitespace after the marker is eaten, forming indented code
+      // is not possible.
+      // No space is also fine, just like a block quote marker.
+      return factorySpace(effects, whitespaceAfter, 'gfmFootnoteDefinitionWhitespace');
+    }
+    return nok(code);
+  }
+
+  /**
+   * After definition prefix.
+   *
+   * ```markdown
+   * > | [^a]: b
+   *           ^
+   * ```
+   *
+   * @type {State}
+   */
+  function whitespaceAfter(code) {
+    // `markdown-rs` has a wrapping token for the prefix that is closed here.
+    return ok(code);
+  }
+}
+
+/**
+ * @this {TokenizeContext}
+ * @type {Tokenizer}
+ */
+function tokenizeDefinitionContinuation(effects, ok, nok) {
+  /// Start of footnote definition continuation.
+  ///
+  /// ```markdown
+  ///   | [^a]: b
+  /// > |     c
+  ///     ^
+  /// ```
+  //
+  // Either a blank line, which is okay, or an indented thing.
+  return effects.check(blankLine, ok, effects.attempt(indent, ok, nok));
+}
+
+/** @type {Exiter} */
+function gfmFootnoteDefinitionEnd(effects) {
+  effects.exit('gfmFootnoteDefinition');
+}
+
+/**
+ * @this {TokenizeContext}
+ * @type {Tokenizer}
+ */
+function tokenizeIndent(effects, ok, nok) {
+  const self = this;
+  return factorySpace(effects, afterPrefix, 'gfmFootnoteDefinitionIndent', 4 + 1);
+
+  /**
+   * @type {State}
+   */
+  function afterPrefix(code) {
+    const tail = self.events[self.events.length - 1];
+    return tail && tail[1].type === 'gfmFootnoteDefinitionIndent' && tail[2].sliceSerialize(tail[1], true).length === 4 ? ok(code) : nok(code);
+  }
+}

node_modules/micromark-extension-gfm-footnote/license

@@ -0,0 +1,22 @@
+(The MIT License)
+
+Copyright (c) 2021 Titus Wormer <tituswormer@gmail.com>
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+'Software'), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

node_modules/micromark-extension-gfm-footnote/package.json

@@ -0,0 +1,132 @@
+{
+  "name": "micromark-extension-gfm-footnote",
+  "version": "2.1.0",
+  "description": "micromark extension to support GFM footnotes",
+  "license": "MIT",
+  "keywords": [
+    "micromark",
+    "micromark-extension",
+    "gfm",
+    "footnote",
+    "note",
+    "definition",
+    "markdown",
+    "unified"
+  ],
+  "repository": "micromark/micromark-extension-gfm-footnote",
+  "bugs": "https://github.com/micromark/micromark-extension-gfm-footnote/issues",
+  "funding": {
+    "type": "opencollective",
+    "url": "https://opencollective.com/unified"
+  },
+  "author": "Titus Wormer <tituswormer@gmail.com> (https://wooorm.com)",
+  "contributors": [
+    "Titus Wormer <tituswormer@gmail.com> (https://wooorm.com)"
+  ],
+  "sideEffects": false,
+  "type": "module",
+  "files": [
+    "dev/",
+    "lib/",
+    "index.d.ts",
+    "index.js"
+  ],
+  "exports": {
+    "development": "./dev/index.js",
+    "default": "./index.js"
+  },
+  "dependencies": {
+    "devlop": "^1.0.0",
+    "micromark-core-commonmark": "^2.0.0",
+    "micromark-factory-space": "^2.0.0",
+    "micromark-util-character": "^2.0.0",
+    "micromark-util-normalize-identifier": "^2.0.0",
+    "micromark-util-sanitize-uri": "^2.0.0",
+    "micromark-util-symbol": "^2.0.0",
+    "micromark-util-types": "^2.0.0"
+  },
+  "devDependencies": {
+    "@types/node": "^20.0.0",
+    "c8": "^10.0.0",
+    "create-gfm-fixtures": "^1.0.0",
+    "micromark": "^4.0.0",
+    "micromark-build": "^2.0.0",
+    "prettier": "^3.0.0",
+    "remark-cli": "^12.0.0",
+    "remark-preset-wooorm": "^10.0.0",
+    "type-coverage": "^2.0.0",
+    "typescript": "^5.0.0",
+    "xo": "^0.58.0"
+  },
+  "scripts": {
+    "prepack": "npm run build && npm run format",
+    "build": "tsc --build --clean && tsc --build && type-coverage && micromark-build",
+    "format": "remark . -qfo && prettier . -w --log-level warn && xo --fix",
+    "test-api-prod": "node --conditions production test/index.js",
+    "test-api-dev": "node --conditions development test/index.js",
+    "test-api": "npm run test-api-dev && npm run test-api-prod",
+    "test-coverage": "c8 --100 --reporter lcov npm run test-api",
+    "test": "npm run build && npm run format && npm run test-coverage"
+  },
+  "prettier": {
+    "bracketSpacing": false,
+    "semi": false,
+    "singleQuote": true,
+    "tabWidth": 2,
+    "trailingComma": "none",
+    "useTabs": false
+  },
+  "remarkConfig": {
+    "plugins": [
+      "remark-preset-wooorm"
+    ]
+  },
+  "typeCoverage": {
+    "atLeast": 100,
+    "detail": true,
+    "ignoreCatch": true,
+    "strict": true
+  },
+  "xo": {
+    "prettier": true,
+    "rules": {
+      "logical-assignment-operators": "off",
+      "unicorn/no-this-assignment": "off",
+      "unicorn/prefer-at": "off",
+      "unicorn/prefer-string-replace-all": "off"
+    },
+    "overrides": [
+      {
+        "files": [
+          "**/*.d.ts"
+        ],
+        "rules": {
+          "@typescript-eslint/array-type": [
+            "error",
+            {
+              "default": "generic"
+            }
+          ],
+          "@typescript-eslint/ban-types": [
+            "error",
+            {
+              "extendDefaults": true
+            }
+          ],
+          "@typescript-eslint/consistent-type-definitions": [
+            "error",
+            "interface"
+          ]
+        }
+      },
+      {
+        "files": [
+          "test/**/*.js"
+        ],
+        "rules": {
+          "no-await-in-loop": 0
+        }
+      }
+    ]
+  }
+}

node_modules/micromark-extension-gfm-footnote/readme.md

@@ -0,0 +1,656 @@
+# micromark-extension-gfm-footnote
+
+[![Build][build-badge]][build]
+[![Coverage][coverage-badge]][coverage]
+[![Downloads][downloads-badge]][downloads]
+[![Size][size-badge]][size]
+[![Sponsors][sponsors-badge]][collective]
+[![Backers][backers-badge]][collective]
+[![Chat][chat-badge]][chat]
+
+[micromark][] extensions to support GFM [footnotes][post].
+
+## Contents
+
+* [What is this?](#what-is-this)
+* [When to use this](#when-to-use-this)
+* [Install](#install)
+* [Use](#use)
+* [API](#api)
+  * [`defaultBackLabel(referenceIndex, rereferenceIndex)`](#defaultbacklabelreferenceindex-rereferenceindex)
+  * [`gfmFootnote()`](#gfmfootnote)
+  * [`gfmFootnoteHtml(options?)`](#gfmfootnotehtmloptions)
+  * [`BackLabelTemplate`](#backlabeltemplate)
+  * [`HtmlOptions`](#htmloptions)
+* [Bugs](#bugs)
+* [Authoring](#authoring)
+* [HTML](#html)
+* [CSS](#css)
+* [Syntax](#syntax)
+* [Types](#types)
+* [Compatibility](#compatibility)
+* [Security](#security)
+* [Related](#related)
+* [Contribute](#contribute)
+* [License](#license)
+
+## What is this?
+
+This package contains extensions that add support for footnotes as enabled by
+GFM to [`micromark`][micromark].
+
+GitHub announced footnotes [on September 30, 2021][post] but did not specify
+them in their GFM spec.
+As they are implemented in their parser and supported in all places where
+other GFM features work, they can be considered part of GFM.
+GitHub employs several other features (such as mentions or frontmatter) that
+are either not in their parser, or not in all places where GFM features work,
+which should not be considered GFM.
+
+The implementation of footnotes on github.com is currently buggy.
+The bugs have been reported on [`cmark-gfm`][cmark-gfm].
+This micromark extension matches github.com except for its bugs.
+
+## When to use this
+
+This project is useful when you want to support footnotes in markdown.
+
+You can use these extensions when you are working with [`micromark`][micromark].
+To support all GFM features, use
+[`micromark-extension-gfm`][micromark-extension-gfm] instead.
+
+When you need a syntax tree, combine this package with
+[`mdast-util-gfm-footnote`][mdast-util-gfm-footnote].
+
+All these packages are used in [`remark-gfm`][remark-gfm], which focusses on
+making it easier to transform content by abstracting these internals away.
+
+## Install
+
+This package is [ESM only][esm].
+In Node.js (version 16+), install with [npm][]:
+
+```sh
+npm install micromark-extension-gfm-footnote
+```
+
+In Deno with [`esm.sh`][esmsh]:
+
+```js
+import {gfmFootnote, gfmFootnoteHtml} from 'https://esm.sh/micromark-extension-gfm-footnote@2'
+```
+
+In browsers with [`esm.sh`][esmsh]:
+
+```html
+<script type="module">
+  import {gfmFootnote, gfmFootnoteHtml} from 'https://esm.sh/micromark-extension-gfm-footnote@2?bundle'
+</script>
+```
+
+## Use
+
+Say our document `example.md` contains:
+
+````markdown
+Using footnotes is fun![^1] They let you reference relevant information without disrupting the flow of what you’re trying to say.[^bignote]
+
+[^1]: This is the first footnote.
+[^bignote]: Here’s one with multiple paragraphs and code.
+
+    Indent paragraphs to include them in the footnote.
+
+    ```
+    my code
+    ```
+
+    Add as many paragraphs as you like.
+
+Text here and here and here.
+[Learn more about markdown and footnotes in markdown](https://docs.github.com/en/github/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#footnotes)
+````
+
+…and our module `example.js` looks as follows:
+
+```js
+import fs from 'node:fs/promises'
+import {micromark} from 'micromark'
+import {gfmFootnote, gfmFootnoteHtml} from 'micromark-extension-gfm-footnote'
+
+const output = micromark(await fs.readFile('example.md'), {
+  extensions: [gfmFootnote()],
+  htmlExtensions: [gfmFootnoteHtml()]
+})
+
+console.log(output)
+```
+
+…now running `node example.js` yields:
+
+```html
+<p>Using footnotes is fun!<sup><a href="#user-content-fn-1" id="user-content-fnref-1" data-footnote-ref="" aria-describedby="footnote-label">1</a></sup> They let you reference relevant information without disrupting the flow of what you’re trying to say.<sup><a href="#user-content-fn-bignote" id="user-content-fnref-bignote" data-footnote-ref="" aria-describedby="footnote-label">2</a></sup></p>
+<p>Text here and here and here.
+<a href="https://docs.github.com/en/github/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#footnotes">Learn more about markdown and footnotes in markdown</a></p>
+<section data-footnotes="" class="footnotes"><h2 id="footnote-label" class="sr-only">Footnotes</h2>
+<ol>
+<li id="user-content-fn-1">
+<p>This is the first footnote. <a href="#user-content-fnref-1" data-footnote-backref="" class="data-footnote-backref" aria-label="Back to content">↩</a></p>
+</li>
+<li id="user-content-fn-bignote">
+<p>Here’s one with multiple paragraphs and code.</p>
+<p>Indent paragraphs to include them in the footnote.</p>
+<pre><code>my code
+</code></pre>
+<p>Add as many paragraphs as you like. <a href="#user-content-fnref-bignote" data-footnote-backref="" class="data-footnote-backref" aria-label="Back to content">↩</a></p>
+</li>
+</ol>
+</section>
+```
+
+## API
+
+This package exports the identifiers
+[`defaultBackLabel`][api-default-back-label],
+[`gfmFootnote`][api-gfm-footnote], and
+[`gfmFootnoteHtml`][api-gfm-footnote-html].
+There is no default export.
+
+The export map supports the [`development` condition][development].
+Run `node --conditions development module.js` to get instrumented dev code.
+Without this condition, production code is loaded.
+
+### `defaultBackLabel(referenceIndex, rereferenceIndex)`
+
+Generate the default label that GitHub uses on backreferences
+([`BackLabelTemplate`][api-back-label-template]).
+
+### `gfmFootnote()`
+
+Create an extension for `micromark` to enable GFM footnote syntax.
+
+###### Returns
+
+Extension for `micromark` that can be passed in `extensions` to enable GFM
+footnote syntax ([`Extension`][micromark-extension]).
+
+### `gfmFootnoteHtml(options?)`
+
+Create an extension for `micromark` to support GFM footnotes when serializing
+to HTML.
+
+###### Parameters
+
+* `options` ([`HtmlOptions`][api-html-options], optional)
+  — configuration
+
+###### Returns
+
+Extension for `micromark` that can be passed in `htmlExtensions` to support GFM
+footnotes when serializing to HTML
+([`HtmlExtension`][micromark-html-extension]).
+
+### `BackLabelTemplate`
+
+Generate a back label dynamically (TypeScript type).
+
+For the following markdown:
+
+```markdown
+Alpha[^micromark], bravo[^micromark], and charlie[^remark].
+
+[^remark]: things about remark
+[^micromark]: things about micromark
+```
+
+This function will be called with:
+
+* `0` and `0` for the backreference from `things about micromark` to
+  `alpha`, as it is the first used definition, and the first call to it
+* `0` and `1` for the backreference from `things about micromark` to
+  `bravo`, as it is the first used definition, and the second call to it
+* `1` and `0` for the backreference from `things about remark` to
+  `charlie`, as it is the second used definition
+
+###### Parameters
+
+* `referenceIndex` (`number`)
+  — index of the definition in the order that they are first referenced,
+  0-indexed
+* `rereferenceIndex` (`number`)
+  — index of calls to the same definition, 0-indexed
+
+###### Returns
+
+Back label to use when linking back from definitions to their reference
+(`string`).
+
+### `HtmlOptions`
+
+Configuration (TypeScript type).
+
+##### Fields
+
+###### `clobberPrefix`
+
+Prefix to use before the `id` attribute on footnotes to prevent them from
+*clobbering* (`string`, default: `'user-content-'`).
+
+Pass `''` for trusted markdown and when you are careful with polyfilling.
+You could pass a different prefix.
+
+DOM clobbering is this:
+
+```html
+<p id="x"></p>
+<script>alert(x) // `x` now refers to the `p#x` DOM element</script>
+```
+
+The above example shows that elements are made available by browsers, by their
+ID, on the `window` object.
+This is a security risk because you might be expecting some other variable at
+that place.
+It can also break polyfills.
+Using a prefix solves these problems.
+
+###### `label`
+
+Textual label to use for the footnotes section (`string`, default:
+`'Footnotes'`).
+
+Change it when the markdown is not in English.
+
+This label is typically hidden visually (assuming a `sr-only` CSS class
+is defined that does that) and so affects screen readers only.
+
+###### `labelAttributes`
+
+Attributes to use on the footnote label (`string`, default:
+`'class="sr-only"'`).
+
+Change it to show the label and add other attributes.
+
+This label is typically hidden visually (assuming an `sr-only` CSS class
+is defined that does that) and so affects screen readers only.
+If you do have such a class, but want to show this section to everyone,
+pass an empty string.
+You can also add different attributes.
+
+> 👉 **Note**: `id="footnote-label"` is always added, because footnote
+> calls use it with `aria-describedby` to provide an accessible label.
+
+###### `labelTagName`
+
+HTML tag name to use for the footnote label element (`string`, default:
+`'h2'`).
+
+Change it to match your document structure.
+
+This label is typically hidden visually (assuming a `sr-only` CSS class
+is defined that does that) and so affects screen readers only.
+
+###### `backLabel`
+
+Textual label to describe the backreference back to footnote calls
+([`BackLabelTemplate`][api-back-label-template] or `string`,
+default: [`defaultBackLabel`][api-default-back-label]).
+
+Change it when the markdown is not in English.
+
+This label is used in the [`aria-label`][aria-label] attribute on each
+backreference (the `↩` links).
+It affects users of assistive technology.
+
+## Bugs
+
+GitHub’s own algorithm to parse footnote definitions contains several bugs.
+These are not present in this project.
+The issues relating to footnote definitions are:
+
+* [Footnote reference call identifiers are trimmed, but definition
+  identifiers aren’t](https://github.com/github/cmark-gfm/issues/237)\
+  — initial and final whitespace in labels causes them not to match
+* [Footnotes are matched case-insensitive, but links keep their casing,
+  breaking them](https://github.com/github/cmark-gfm/issues/239)\
+  — using uppercase (or any character that will be percent encoded) in
+  identifiers breaks links
+* [Colons in footnotes generate links w/o
+  `href`](https://github.com/github/cmark-gfm/issues/250)\
+  — colons in identifiers generate broken links
+* [Character escape of `]` does not work in footnote
+  identifiers](https://github.com/github/cmark-gfm/issues/240)\
+  — some character escapes don’t work
+* [Footnotes in links are
+  broken](https://github.com/github/cmark-gfm/issues/249)\
+  — while `CommonMark` prevents links in links, GitHub does not prevent
+  footnotes (which turn into links) in links
+* [Footnote-like brackets around image, break that
+  image](https://github.com/github/cmark-gfm/issues/275)\
+  — images can’t be used in what looks like a footnote call
+* [GFM footnotes: line ending in footnote definition label causes text to
+  disappear](https://github.com/github/cmark-gfm/issues/282)\
+  — line endings in footnote definitions cause text to disappear
+
+## Authoring
+
+When authoring markdown with footnotes it’s recommended to use words instead
+of numbers (or letters or anything with an order) as identifiers.
+That makes it easier to reuse and reorder footnotes.
+
+It’s recommended to place footnotes definitions at the bottom of the document.
+
+## HTML
+
+GFM footnotes do not, on their own, relate to anything in HTML.
+When a footnote reference matches with a definition, they each relate to several
+elements in HTML.
+
+The reference relates to `<sup>` and `<a>` elements in HTML:
+
+```html
+<sup><a href="#user-content-fn-x" id="user-content-fnref-x" data-footnote-ref="" aria-describedby="footnote-label">1</a></sup></p>
+```
+
+…where `x` is the identifier used in the markdown source and `1` the number of
+corresponding, listed, definition.
+
+See [*§ 4.5.19 The `sub` and `sup` elements*][html-sup],
+[*§ 4.5.1 The `a` element*][html-a], and
+[*§ 3.2.6.6 Embedding custom non-visible data with the `data-*`
+attributes*][html-data]
+in the HTML spec, and
+[*§ 6.8 `aria-describedby` property*][aria-describedby]
+in WAI-ARIA, for more info.
+
+When one or more definitions are referenced, a footnote section is generated at
+the end of the document, using `<section>`, `<h2>`, and `<ol>` elements:
+
+```html
+<section data-footnotes="" class="footnotes"><h2 id="footnote-label" class="sr-only">Footnotes</h2>
+<ol>…</ol>
+</section>
+```
+
+Each definition is generated as a `<li>` in the `<ol>` in the order they were
+first referenced:
+
+```html
+<li id="user-content-fn-1">…</li>
+```
+
+Backreferences are injected at the end of the first paragraph, or, when there
+is no paragraph, at the end of the definition.
+When a definition is referenced multiple times, multiple backreferences are
+generated.
+Further backreferences use an extra counter in the `href` attribute and
+visually in a `<span>` after `↩`.
+
+```html
+<a href="#user-content-fnref-1" data-footnote-backref="" class="data-footnote-backref" aria-label="Back to content">↩</a> <a href="#user-content-fnref-1-2" data-footnote-backref="" class="data-footnote-backref" aria-label="Back to content">↩<sup>2</sup></a>
+```
+
+See
+[*§ 4.5.1 The `a` element*][html-a],
+[*§ 4.3.6 The `h1`, `h2`, `h3`, `h4`, `h5`, and `h6` elements*][html-h],
+[*§ 4.4.8 The `li` element*][html-li],
+[*§ 4.4.5 The `ol` element*][html-ol],
+[*§ 4.4.1 The `p` element*][html-p],
+[*§ 4.3.3 The `section` element*][html-section], and
+[*§ 4.5.19 The `sub` and `sup` elements*][html-sup]
+in the HTML spec, and
+[*§ 6.8 `aria-label` property*][aria-label]
+in WAI-ARIA, for more info.
+
+## CSS
+
+The following CSS is needed to make footnotes look a bit like GitHub (and fixes
+a bug).
+For the complete actual CSS see
+[`sindresorhus/github-markdown-css`](https://github.com/sindresorhus/github-markdown-css).
+
+```css
+/* Style the footnotes section. */
+.footnotes {
+  font-size: smaller;
+  color: #8b949e;
+  border-top: 1px solid #30363d;
+}
+
+/* Hide the section label for visual users. */
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  word-wrap: normal;
+  border: 0;
+}
+
+/* Place `[` and `]` around footnote references. */
+[data-footnote-ref]::before {
+  content: '[';
+}
+
+[data-footnote-ref]::after {
+  content: ']';
+}
+```
+
+## Syntax
+
+Footnotes form with, roughly, the following BNF:
+
+```bnf
+gfm_footnote_reference ::= gfm_footnote_label
+
+gfm_footnote_definition_start ::= gfm_footnote_label ':' *space_or_tab
+; Restriction: blank line allowed.
+gfm_footnote_definition_cont ::= 4(space_or_tab)
+
+; Restriction: maximum `999` codes between `^` and `]`.
+gfm_footnote_label ::= '[' '^' 1*(gfm_footnote_label_byte | gfm_footnote_label_escape) ']'
+gfm_footnote_label_byte ::= text - '[' - '\\' - ']'
+gfm_footnote_label_escape ::= '\\' ['[' | '\\' | ']']
+
+; Any byte (u8)
+byte ::= 0x00..=0xFFFF
+space_or_tab ::= '\t' | ' '
+eol ::= '\n' | '\r' | '\r\n'
+line ::= byte - eol
+text ::= line - space_or_tab
+```
+
+Further lines after `gfm_footnote_definition_start` that are not prefixed with
+`gfm_footnote_definition_cont` cause the footnote definition to be exited,
+except when those lines are lazy continuation or blank.
+Like so many things in markdown, footnote definition too are complex.
+See [*§ Phase 1: block structure* in `CommonMark`][commonmark-block] for more
+on parsing details.
+
+The identifiers in the `label` parts are interpreted as the
+[string][micromark-content-types] content type.
+That means that character escapes and character references are allowed.
+
+Definitions match to references through identifiers.
+To match, both labels must be equal after normalizing with
+[`normalizeIdentifier`][micromark-normalize-identifier].
+One definition can match to multiple calls.
+Multiple definitions with the same, normalized, identifier are ignored: the
+first definition is preferred.
+To illustrate, the definition with the content of `x` wins:
+
+```markdown
+[^a]: x
+[^a]: y
+
+[^a]
+```
+
+Importantly, while labels *can* include [string][micromark-content-types]
+content (character escapes and character references), these are not considered
+when matching.
+To illustrate, neither definition matches the reference:
+
+```markdown
+[^a&amp;b]: x
+[^a\&b]: y
+
+[^a&b]
+```
+
+Because footnote definitions are containers (like block quotes and list items),
+they can contain more footnote definitions.
+They can even include references to themselves.
+
+## Types
+
+This package is fully typed with [TypeScript][].
+It exports the additional types [`BackLabelTemplate`][api-back-label-template]
+and [`HtmlOptions`][api-html-options].
+
+## Compatibility
+
+Projects maintained by the unified collective are compatible with maintained
+versions of Node.js.
+
+When we cut a new major release, we drop support for unmaintained versions of
+Node.
+This means we try to keep the current release line,
+`micromark-extension-gfm-footnote@^2`, compatible with Node.js 16.
+
+This package works with `micromark` version `3` and later.
+
+## Security
+
+This package is safe.
+Setting `clobberPrefix = ''` is dangerous, it opens you up to DOM clobbering.
+The `labelTagName` and `labelAttributes` options are unsafe when used with user
+content, they allow defining arbitrary HTML.
+
+## Related
+
+* [`micromark-extension-gfm`][micromark-extension-gfm]
+  — support all of GFM
+* [`mdast-util-gfm-footnote`][mdast-util-gfm-footnote]
+  — support all of GFM in mdast
+* [`mdast-util-gfm`][mdast-util-gfm]
+  — support all of GFM in mdast
+* [`remark-gfm`][remark-gfm]
+  — support all of GFM in remark
+
+## Contribute
+
+See [`contributing.md` in `micromark/.github`][contributing] for ways to get
+started.
+See [`support.md`][support] for ways to get help.
+
+This project has a [code of conduct][coc].
+By interacting with this repository, organization, or community you agree to
+abide by its terms.
+
+## License
+
+[MIT][license] © [Titus Wormer][author]
+
+<!-- Definitions -->
+
+[build-badge]: https://github.com/micromark/micromark-extension-gfm-footnote/workflows/main/badge.svg
+
+[build]: https://github.com/micromark/micromark-extension-gfm-footnote/actions
+
+[coverage-badge]: https://img.shields.io/codecov/c/github/micromark/micromark-extension-gfm-footnote.svg
+
+[coverage]: https://codecov.io/github/micromark/micromark-extension-gfm-footnote
+
+[downloads-badge]: https://img.shields.io/npm/dm/micromark-extension-gfm-footnote.svg
+
+[downloads]: https://www.npmjs.com/package/micromark-extension-gfm-footnote
+
+[size-badge]: https://img.shields.io/badge/dynamic/json?label=minzipped%20size&query=$.size.compressedSize&url=https://deno.bundlejs.com/?q=micromark-extension-gfm-footnote
+
+[size]: https://bundlejs.com/?q=micromark-extension-gfm-footnote
+
+[sponsors-badge]: https://opencollective.com/unified/sponsors/badge.svg
+
+[backers-badge]: https://opencollective.com/unified/backers/badge.svg
+
+[collective]: https://opencollective.com/unified
+
+[chat-badge]: https://img.shields.io/badge/chat-discussions-success.svg
+
+[chat]: https://github.com/micromark/micromark/discussions
+
+[npm]: https://docs.npmjs.com/cli/install
+
+[esmsh]: https://esm.sh
+
+[license]: license
+
+[author]: https://wooorm.com
+
+[contributing]: https://github.com/micromark/.github/blob/main/contributing.md
+
+[support]: https://github.com/micromark/.github/blob/main/support.md
+
+[coc]: https://github.com/micromark/.github/blob/main/code-of-conduct.md
+
+[esm]: https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c
+
+[typescript]: https://www.typescriptlang.org
+
+[development]: https://nodejs.org/api/packages.html#packages_resolving_user_conditions
+
+[micromark]: https://github.com/micromark/micromark
+
+[micromark-content-types]: https://github.com/micromark/micromark#content-types
+
+[micromark-extension]: https://github.com/micromark/micromark#syntaxextension
+
+[micromark-html-extension]: https://github.com/micromark/micromark#htmlextension
+
+[micromark-normalize-identifier]: https://github.com/micromark/micromark/tree/main/packages/micromark-util-normalize-identifier
+
+[micromark-extension-gfm]: https://github.com/micromark/micromark-extension-gfm
+
+[mdast-util-gfm-footnote]: https://github.com/syntax-tree/mdast-util-gfm-footnote
+
+[mdast-util-gfm]: https://github.com/syntax-tree/mdast-util-gfm
+
+[remark-gfm]: https://github.com/remarkjs/remark-gfm
+
+[post]: https://github.blog/changelog/2021-09-30-footnotes-now-supported-in-markdown-fields/
+
+[cmark-gfm]: https://github.com/github/cmark-gfm
+
+[commonmark-block]: https://spec.commonmark.org/0.30/#phase-1-block-structure
+
+[html-a]: https://html.spec.whatwg.org/multipage/text-level-semantics.html#the-a-element
+
+[html-data]: https://html.spec.whatwg.org/multipage/dom.html#embedding-custom-non-visible-data-with-the-data-*-attributes
+
+[html-h]: https://html.spec.whatwg.org/multipage/sections.html#the-h1,-h2,-h3,-h4,-h5,-and-h6-elements
+
+[html-li]: https://html.spec.whatwg.org/multipage/grouping-content.html#the-li-element
+
+[html-ol]: https://html.spec.whatwg.org/multipage/grouping-content.html#the-ol-element
+
+[html-p]: https://html.spec.whatwg.org/multipage/grouping-content.html#the-p-element
+
+[html-section]: https://html.spec.whatwg.org/multipage/sections.html#the-section-element
+
+[html-sup]: https://html.spec.whatwg.org/multipage/text-level-semantics.html#the-sub-and-sup-elements
+
+[aria-describedby]: https://w3c.github.io/aria/#aria-describedby
+
+[aria-label]: https://w3c.github.io/aria/#aria-label
+
+[api-gfm-footnote]: #gfmfootnote
+
+[api-gfm-footnote-html]: #gfmfootnotehtmloptions
+
+[api-html-options]: #htmloptions
+
+[api-default-back-label]: #defaultbacklabelreferenceindex-rereferenceindex
+
+[api-back-label-template]: #backlabeltemplate