This is the flexible implementation of a field: it can easily be extended because it stores its data in a hash and the constructor (new) and initializer (init) are split. However, you pay the price in performance. Mail::Message::Field::Fast is faster (as the name predicts).
If you stick to this flexible class of header fields, you have a bit more facilities than with Mail::Message::Field::Fast. Amongst it, you can specify options with the creation. Possible arguments:
ass a LINE as it could be found in a file: a (possibly folded) line which is terminated by a new-line.
new NAME, (BODY|OBJECTS), [ATTRIBUTES], OPTIONS
A set of values which shape the line.
To be able to distinguish the different parameters, you will have to specify the OPTIONS as ARRAY of option pairs, or HASH of options. The ATTRIBUTES are a flat list of key-value pairs. The body is specified as one BODY string, one OBJECT, or a reference to an array of OBJECTS. See Mail::Message::Field:
Reference to array with list of key-value pairs representing attributes, or reference to a hash containing these pairs. This is an alternative notation for specifying ATTRIBUTES directly as method arguments.
A new field is being created which does contain characters not permitted by the RFCs. Using this field in messages may break other e-mail clients or transfer agents, and therefore mutulate or extinguish your message.
Fatal error: the specific package (or one of its superclasses) does not implement this method where it should. This message means that some other related classes do implement this method however the class at hand does not. Probably you should investigate this and probably inform the author of the package.