def plus(other)
      if other.is_a?(Sass::Script::Value::Number) || other.is_a?(Sass::Script::Value::Color)
        piecewise(other, :+)
      else
        super
      end
    end
def plus(other)
      if other.is_a?(Sass::Script::Value::Number) || other.is_a?(Sass::Script::Value::Color)
        piecewise(other, :+)
      else
        super
      end
    end
The SassScript `+` operation.
 Its functionality depends on the type of its argument:

 {Number}
 : Adds the number to each of the RGB color channels.

 {Color}
 : Adds each of the RGB color channels together.

 {Value}
 : See {Value::Base#plus}.

 @param other [Value] The right-hand side of the operator
 @return [Color] The resulting color
 @raise [Sass::SyntaxError] if `other` is a number with units