code: def match_default(self, el):
          
  
          match = False
  
          # Find this input's form
          form = None
          parent = self.get_parent(el, no_iframe=True)
          while parent and form is None:
              if self.get_tag(parent) == 'form' and self.is_html_tag(parent):
                  form = parent
              else:
                  parent = self.get_parent(parent, no_iframe=True)
  
          # Look in form cache to see if we've already located its default button
          found_form = False
          for f, t in self.cached_default_forms:
              if f is form:
                  found_form = True
                  if t is el:
                      match = True
                  break
  
          # We didn't have the form cached, so look for its default button
          if not found_form:
              for child in self.get_descendants(form, no_iframe=True):
                  name = self.get_tag(child)
                  # Can't do nested forms (haven't figured out why we never hit this)
                  if name == 'form':  # pragma: no cover
                      break
                  if name in ('input', 'button'):
                      v = self.get_attribute_by_name(child, 'type', '')
                      if v and util.lower(v) == 'submit':
                          self.cached_default_forms.append([form, child])
                          if el is child:
                              match = True
                          break
          return match
docs: Match default.