Text files can be in plain text format, RTF format, and RTFD format. They can be comma- or tab-separated. This is documented under “Add Group from File…” in the “Snippet Groups” section of the help. There is no provision for multi-line snippets. Here is a list of the special characters:

%Y Date: Year: 4 digits (2006)
%y Date: Year: 2 digits (06)
%B Date: Month: long name (January)
%b Date: Month: short name (Jan)
%m Date: Month: 2 digits (01)
%1m Date: Month: 1-2 digits (1)
%A Date: Day: long name (Monday)
%a Date: Day: short name (Mon)
%d Date: Day: 2 digits (01)
%e Date: Day: 1 digit (1)

%H Time: Hour: 24 hour clock, 2 digits (14)
%I Time: Hour: (capital letter i) 12 hour clock, 2 digits (09)
%1H Time: Hour: 24 hour clock, 1-2 digits (9)
%1I Time: Hour: (capital letter i) 12 hour clock, 1-2 digits (5)
%M Time: Minute: 2 digits (09)
%1M Time: Minute: 1-2 digits (9)
%S Time: Second: 2 digits (05)
%1S Time: Second: 1-2 digits (5)

%snippet:% : insert abbreviation here

%clipboard : insert clipboard contents here

%| : (shift-\) position cursor here once snippet is pasted
% : cursor right
%^ : (shift-6) cursor up
%v : (letter v) cursor down
%+ : keep delimiter
%- : abandon delimiter

@Erik J. Barzeski: Sorry, I was being facetious about being arrested. (I would be severely traumatized if I was kicked out!)

If an Apple Store employee tells you that no photos are allowed, you should respect that. They are doing their job. Most retail stores have some policy against photography. I think they are primarily worried that competitors will try to copy their store designs. (It would be a hilarious failure if they tried copying Apple…) I’m sure there are also issues of consumer privacy.

Also, I can not find any documentation for the syntax of text files. (shortcut)(TAB)(snippet) appears to work, but how about multi-line snippets, inserting the clipboard, etc.?