Node:About Aux-Items, Next:Predefined Aux-Item Types, Up:The Aux-Item List
Aux-items were introduced in protocol version 10 as a mechanism for extending the conference, text and server information structures without changing the protocol. Persons were excluded since nobody could figure out a case where setting an aux-item on the mailbox wasn't as good as setting it on the person (another reason was that I was fed up writing aux-item code by the time they were working on texts and conferences.)
The exact structure of an aux item is specified elsewhere
(see Auxiliary Information). The important fields here are the
aux-no, tag and data fields.
The aux-no field is used to identify an item. The
aux-no together with a text or conference number uniquely
identifies a particular aux item. Items are numbered from one and up
within each item list. Once assigned, the aux-no for an item
is never changed. New items are guaranteed to be assigned numbers that
have never been used before within a particular list.
The tag field identifies the type of aux item. It is used by
the server and by clients to figure out how to interpret the data
field, and by the server to decide if the item needs special
treatment.
The data field is a simple string. The meaning of the string
is determined by the tag field, but since it is a string,
clients that have no understanding of the contents can successfully
parse the item anyway (in contrast to items in the misc-info list.)