whole_func_string: function isRIdent(node) {
      return node &&
             node.type &&
             node.type === T.IDENT &&
             node.content === 'R'
  }
func_code_string: function isRIdent(node) {
      return node &&
             node.type &&
             node.type === T.IDENT &&
             node.content === 'R'
  }
func_documentation_string: whether a node is and identifier and its content is `R`