class Builder::XmlBase

def method_missing(sym, *args, &block)

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