class Sass::Selector::AbstractSequence

def has_placeholder?

Checks recursively.
Whether or not this selector sequence contains a placeholder selector. 
def has_placeholder?
  @has_placeholder ||= members.any? do |m|
    next m.has_placeholder? if m.is_a?(AbstractSequence)
    next m.selector && m.selector.has_placeholder? if m.is_a?(Pseudo)
    m.is_a?(Placeholder)
  end
end