Supplying undef for a hashref, or an empty set of values, effectively clears the object. The self object is returned. Extract parameter info from a structured field, and return it as a hash reference. This has been provided as a public method to support backwards compatibility, but you probably shouldn't use it. Parse the string into the instance.
Any previous information is wiped.
The self object is returned. May also be used as a constructor. Return the given parameter, or undef if it isn't there. Convert the field to a string, and return it. Return the tag for this field.