class Sass::Script::Tree::ListLiteral

def element_needs_parens?(element)

when serialized to Sass.
Returns whether an element in the list should be wrapped in parentheses 
def element_needs_parens?(element)
  if element.is_a?(ListLiteral)
    return false if element.elements.length < 2
    return false if element.bracketed
    return Sass::Script::Parser.precedence_of(element.separator || :space) <=
           Sass::Script::Parser.precedence_of(separator || :space)
  end
  return false unless separator == :space
  if element.is_a?(UnaryOperation)
    return element.operator == :minus || element.operator == :plus
  end
  return false unless element.is_a?(Operation)
  return true unless element.operator == :div
  !(is_literal_number?(element.operand1) && is_literal_number?(element.operand2))
end