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#### 11.7.4 Headers

Internally Gnus uses a format for storing article headers that corresponds to the NOV format in a mysterious fashion. One could almost suspect that the author looked at the NOV specification and just shamelessly stole the entire thing, and one would be right.

Header is a severely overloaded term. “Header” is used in RFC 1036 to talk about lines in the head of an article (e.g., `From`). It is used by many people as a synonym for “head”—“the header and the body”. (That should be avoided, in my opinion.) And Gnus uses a format internally that it calls “header”, which is what I’m talking about here. This is a 9-element vector, basically, with each header (ouch) having one slot.

These slots are, in order: `number`, `subject`, `from`, `date`, `id`, `references`, `chars`, `lines`, `xref`, and `extra`. There are macros for accessing and setting these slots—they all have predictable names beginning with `mail-header-` and `mail-header-set-`, respectively.

All these slots contain strings, except the `extra` slot, which contains an alist of header/value pairs (see To From Newsgroups).