def method_missing(sym, *args, &block)
      cache_method_call(sym) if ::Builder::XmlBase.cache_method_calls
      tag!(sym, *args, &block)
    end
def method_missing(sym, *args, &block)
      cache_method_call(sym) if ::Builder::XmlBase.cache_method_calls
      tag!(sym, *args, &block)
    end
Create XML markup based on the name of the method.  This method
 is never invoked directly, but is called for each markup method
 in the markup block that isn't cached.