Description:
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There exists a neat PI to generate date/time stamps[1].
Zend Framework already use it for their documentations, and it could 
replace the newly-introduced entity trick[2].

Worth looking into.

NOTE: Docbook-XSL supports several format characters, but these do not 
match the date() format characters (see for example the 'S' character)!
We should probably only implements the chars defined in the "spec", 
using some sort of "lookup array" from the dbtimestamp format character 
to date() format character.

[1] http://www.sagehill.net/docbookxsl/Datetime.html
[2] http://svn.php.net/viewvc?view=revision&revision=293139

Reproduce code:
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<para>This document was generated <?dbtimestamp format="Y"?>.</para>