class Sass::Tree::PropNode

def val_to_sass_comma(node, opts)
  return node unless node.is_a?(Sass::Script::Tree::Operation)
  return val_to_sass_concat(node, opts) unless node.operator == :comma
  Sass::Script::Tree::Operation.new(
    val_to_sass_concat(node.operand1, opts),
    val_to_sass_comma(node.operand2, opts),
    node.operator)
end