nl_tokens: fnparam means that this identifier is being defined as a function argument ( see identifier () )
pl_tokens: function optionalidentifier ( fnparam ) { if ( nexttoken . identifier ) { advance ( ) ; if ( token . reserved && ! option . es5 ) { // `undefined` as a function param is a common pattern to protect // against the case when somebody does `undefined = true` and // help with minification. More info: https://gist.github.com/315916 if ( ! fnparam || token . <mask> !== 'undefined' ) { warning ( "Expected an identifier and instead saw '{a}' (a reserved word)." , token , token . id ) ; } } return token . value ; } }