app/node_modules/markdown-it/lib/rules_block/html_block.mjs

// HTML block

import block_names from '../common/html_blocks.mjs'
import { HTML_OPEN_CLOSE_TAG_RE } from '../common/html_re.mjs'

// An array of opening and corresponding closing sequences for html tags,
// last argument defines whether it can terminate a paragraph or not
//
const HTML_SEQUENCES = [
  [/^<(script|pre|style|textarea)(?=(\s|>|$))/i, /<\/(script|pre|style|textarea)>/i, true],
  [/^<!--/,        /-->/,   true],
  [/^<\?/,         /\?>/,   true],
  [/^<![A-Z]/,     />/,     true],
  [/^<!\[CDATA\[/, /\]\]>/, true],
  [new RegExp('^</?(' + block_names.join('|') + ')(?=(\\s|/?>|$))', 'i'), /^$/, true],
  [new RegExp(HTML_OPEN_CLOSE_TAG_RE.source + '\\s*$'),  /^$/, false]
]

export default function html_block (state, startLine, endLine, silent) {
  let pos = state.bMarks[startLine] + state.tShift[startLine]
  let max = state.eMarks[startLine]

  // if it's indented more than 3 spaces, it should be a code block
  if (state.sCount[startLine] - state.blkIndent >= 4) { return false }

  if (!state.md.options.html) { return false }

  if (state.src.charCodeAt(pos) !== 0x3C/* < */) { return false }

  let lineText = state.src.slice(pos, max)

  let i = 0
  for (; i < HTML_SEQUENCES.length; i++) {
    if (HTML_SEQUENCES[i][0].test(lineText)) { break }
  }
  if (i === HTML_SEQUENCES.length) { return false }

  if (silent) {
    // true if this sequence can be a terminator, false otherwise
    return HTML_SEQUENCES[i][2]
  }

  let nextLine = startLine + 1

  // If we are here - we detected HTML block.
  // Let's roll down till block end.
  if (!HTML_SEQUENCES[i][1].test(lineText)) {
    for (; nextLine < endLine; nextLine++) {
      if (state.sCount[nextLine] < state.blkIndent) { break }

      pos = state.bMarks[nextLine] + state.tShift[nextLine]
      max = state.eMarks[nextLine]
      lineText = state.src.slice(pos, max)

      if (HTML_SEQUENCES[i][1].test(lineText)) {
        if (lineText.length !== 0) { nextLine++ }
        break
      }
    }
  }

  state.line = nextLine

  const token   = state.push('html_block', '', 0)
  token.map     = [startLine, nextLine]
  token.content = state.getLines(startLine, nextLine, state.blkIndent, true)

  return true
}