nl_tokens: Optimized for sparse arrays if separator is .
pl_tokens: function SparseJoin ( array , keys , convert ) { var keys_length = keys . length ; var elements = new InternalArray ( keys_length ) ; for ( var i = 0 ; i < keys_length ; i ++ ) { var e = <mask> [ keys [ i ] ] ; elements [ i ] = IS_STRING ( e ) ? e : convert ( e ) ; } return % StringBuilderConcat ( elements , keys_length , '' ) ; }