nl_tokens: ECMA - 262 section 15 . 5 . 4 . 6
pl_tokens: function StringConcat ( <mask> /* and more */ ) { // length == 1 "use strict" ; CHECK_OBJECT_COERCIBLE ( this , "String.prototype.concat" ) ; var s = TO_STRING ( this ) ; var len = arguments . length ; for ( var i = 0 ; i < len ; ++ i ) { s = s + TO_STRING ( arguments [ i ] ) ; } return s ; }