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

// Horizontal rule

import { isSpace } from '../common/utils.mjs'

export default function hr (state, startLine, endLine, silent) {
  const 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 }

  let pos = state.bMarks[startLine] + state.tShift[startLine]
  const marker = state.src.charCodeAt(pos++)

  // Check hr marker
  if (marker !== 0x2A/* * */ &&
      marker !== 0x2D/* - */ &&
      marker !== 0x5F/* _ */) {
    return false
  }

  // markers can be mixed with spaces, but there should be at least 3 of them

  let cnt = 1
  while (pos < max) {
    const ch = state.src.charCodeAt(pos++)
    if (ch !== marker && !isSpace(ch)) { return false }
    if (ch === marker) { cnt++ }
  }

  if (cnt < 3) { return false }

  if (silent) { return true }

  state.line = startLine + 1

  const token  = state.push('hr', 'hr', 0)
  token.map    = [startLine, state.line]
  token.markup = Array(cnt + 1).join(String.fromCharCode(marker))

  return true
}