studyArena/packages/mathml2omml/src/parse-stringify/stringify.js

function attrString(attribs) {
  const buff = []
  for (const key in attribs) {
    buff.push(`${key}="${attribs[key]}"`)
  }
  if (!buff.length) {
    return ''
  }
  return ` ${buff.join(' ')}`
}

function escapeXmlText(str) {
  return str.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;')
}

function stringify(buff, doc) {
  switch (doc.type) {
    case 'text':
      return buff + escapeXmlText(doc.data)
    case 'tag': {
      const voidElement =
        doc.voidElement || (!doc.children.length && doc.attribs['xml:space'] !== 'preserve')
      buff += `<${doc.name}${doc.attribs ? attrString(doc.attribs) : ''}${voidElement ? '/>' : '>'}`
      if (voidElement) {
        return buff
      }
      return `${buff + doc.children.reduce(stringify, '')}</${doc.name}>`
    }
    case 'comment':
      buff += `<!--${doc.comment}-->`
      return buff
  }
}

export function stringifyDoc(doc) {
  return doc.reduce((token, rootEl) => token + stringify('', rootEl), '')
}