code: function () {
                  var negate, p = input.charAt(i + 1);
  
                  if (input.charAt(i) === '-' && (p === '@' || p === '(')) { negate = $('-') }
                  var o = $(this.sub) || $(this.entities.dimension) ||
                          $(this.entities.color) || $(this.entities.variable) ||
                          $(this.entities.call);
                  return negate ? new(tree.Operation)('*', [new(tree.Dimension)(-1), o])
                                : o;
              }
docs: An operand is anything that can be part of an operation, such as a Color, or a Variable