code: def _get_list_keys(schema_node):
          '''_get_list_keys
  
          Low-level api: Given a schema node, in particular, a list type schema
          node, it returns a list of keys.
  
          Parameters
          ----------
  
          schema_node : `Element`
              A schema node.
  
          Returns
          -------
  
          list
              A list of tags of keys in `{url}tagname` notation.
          '''
  
          nodes = list(filter(lambda x: x.get('is_key'),
                              schema_node.getchildren()))
          return [n.tag for n in nodesf _get_list_keys(schema_node):
          '''_get_list_keys
  
          Low-level api: Given a schema node, in particular, a list type schema
          node, it returns a list of keys.
  
          Parameters
          ----------
  
          schema_node : `Element`
              A schema node.
  
          Returns
          -------
  
          list
              A list of tags of keys in `{url}tagname` notation.
          '''
  
          nodes = list(filter(lambda x: x.get('is_key'),
                              schema_node.getchildren()))
          return [n.tag for n in nodes]
docs: _get_list_keys
  
          Low-level api: Given a schema node, in particular, a list type schema
          node, it returns a list of keys.
  
          Parameters
          ----------
  
          schema_node : `Element`
              A schema node.
  
          Returns
          -------
  
          list
              A list of tags of keys in `{url}tagname` notation.