docs: def _has_xml_encode(self, content):
          """Check XML encoding."""
  
          encode = None
  
          m = RE_XML_START.match(content)
          if m:
              if m.group(1):
                  m2 = RE_XML_ENCODE.match(m.group(1))
  
                  if m2:
                      enc = m2.group(2).decode('ascii')
  
                      try:
                          codecs.getencoder(enc)
                          encode = enc
                      except LookupError:
                          pass
              else:
                  if m.group(2):
                      enc = 'utf-32-be'
                      text = m.group(2)
                  elif m.group(3):
                      enc = 'utf-32-le'
                      text = m.group(3)
                  elif m.group(4):
                      enc = 'utf-16-be'
                      text = m.group(4)
                  elif m.group(5):
                      enc = 'utf-16-le'
                      text = m.group(5)
                  try:
                      m2 = RE_XML_ENCODE_U.match(text.decode(enc))
                  except Exception:  # pragma: no cover
                      m2 = None
  
                  if m2:
                      enc = m2.group(2)
  
                      try:
                          codecs.getencoder(enc)
                          encode = enc
                      except Exception:
                          pass
  
          return encode