docs: def clean_texmath(txt):
      """
      clean tex math string, preserving control sequences
      (incluing \n, so also '\nu') inside $ $, while allowing
      \n and \t to be meaningful in the text string
      """
      s = "%s " % txt
      out = []
      i = 0
      while i < len(s)-1:
          if s[i] == '\\' and s[i+1] in ('n', 't'):
              if s[i+1] == 'n':
                  out.append('\n')
              elif s[i+1] == 't':
                  out.append('\t')
              i += 1
          elif s[i] == '$':
              j = s[i+1:].find('$')
              if j < 0:
                  j = len(s)
              out.append(s[i:j+2])
              i += j+2
          else:
              out.append(s[i])
          i += 1
          if i > 5000:
              break
      return ''.join(out).strip()