docs: def get_requires(self, api=None, profile=None, support=None):
          """Returns filtered list of Require objects in this registry
  
          :param str api: Return Require objects with this api name or None to
                          return all Require objects.
          :param str profile: Return Require objects with this profile or None
                              to return all Require objects.
          :param str support: Return Require objects with this extension support
                              string or None to return all Require objects.
          :return: list of Require objects
          """
          out = []
          for ft in self.get_features(api):
              out.extend(ft.get_requires(profile))
          for ext in self.extensions.values():
              # Filter extension support
              if support and support not in ext.supported:
                  continue
              out.extend(ext.get_requires(api, profile))
          return out