class Temple::HTML::Filter

def contains_nonempty_static?(exp)
  case exp.first
  when :multi
    exp[1..-1].any? {|e| contains_nonempty_static?(e) }
  when :escape
    contains_nonempty_static?(exp.last)
  when :static
    !exp.last.empty?
  else
    false
  end
end