nl_tokens: An operand is anything that can be part of an operation such as a Color or a Variable
pl_tokens: function ( ) { var entities = this . entities , negate ; if ( parserInput . peek ( / ^-[@\$\(] / ) ) { negate = parserInput . $char ( '-' ) ; } var o = this . sub ( ) || entities . dimension ( ) || entities . <mask> ( ) || entities . variable ( ) || entities . property ( ) || entities . call ( ) || entities . quoted ( true ) || entities . colorKeyword ( ) || entities . mixinLookup ( ) ; if ( negate ) { o . parensInOp = true ; o = new ( tree . Negative ) ( o ) ; } return o ; }