class Sanitize::CSS

def property!(prop)
  name = prop[:name].downcase
  # Preserve IE * and _ hacks if desired.
  if @config[:allow_hacks]
    name.slice!(0) if /\A[*_]/.match?(name)
  end
  return nil unless @config[:properties].include?(name)
  nodes = prop[:children].dup
  combined_value = +""
  nodes.each do |child|
    value = child[:value]
    case child[:node]
    when :ident
      combined_value << value.downcase if String === value
    when :function
      if child.key?(:name)
        name = child[:name].downcase
        if name == "url"
          return nil unless valid_url?(child)
        end
        if image_function?(name)
          return nil unless valid_image?(child)
        end
        combined_value << name
        return nil if name == "expression" || combined_value == "expression"
      end
      if Array === value
        nodes.concat(value)
      elsif String === value
        lowercase_value = value.downcase
        combined_value << lowercase_value
        return nil if lowercase_value == "expression" || combined_value == "expression"
      end
    when :url
      return nil unless valid_url?(child)
    when :bad_url
      return nil
    end
  end
  prop
end