function visitor( node ) {
			var id;

			debug( 'Found a definition: %s', node.identifier );
			if ( RE_STDLIB.test( node.identifier ) ) {
				debug( 'Found a package identifier.' );
				id = replace( node.identifier, '@', '%40' );

				debug( 'Current URL: %s', node.url );
				node.url = BASE_URL + opts.branch + '/lib/node_modules/' + id;

				debug( 'Resolved URL: %s', node.url );
			}
		}
Callback invoked upon finding a matching node.

@private
@param {Node} node - reference node