class Sanitize::CSS

def tree!(tree)
  tree.map! do |node|
    next nil if node.nil?
    case node[:node]
    when :at_rule
      next at_rule!(node)
    when :comment
      next node if @config[:allow_comments]
    when :property
      next property!(node)
    when :style_rule
      tree!(node[:children])
      next node
    when :whitespace
      next node
    end
    nil
  end
  tree
end