<listitem override="B"> ignored?

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

It appears that override is ignored:

http://docbook.org/tdg/en/html/listitem.html
Override specifies the keyword for the type of mark to be used on this
ListItem instead of the mark currently in use for the list.

so I expected
<itemizedlist>
<listitem override="B">...
<listitem override="A">...
<listitem override="Z">...
</itemizedlist>

to be rendered

~ B. ...
~ A. ...
~ Z. ...

this expectation is reinforced by
http://docbook.org/tdg/en/html/itemizedlist.html

alas, I do not observe this, I see the standard bullets instead.

So, how do I specify the item labels in my lists?

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.6 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iD8DBQFH0FKwPp1Qsf2qnMcRAr+7AJ0Y6kEz7/qroRd/PFGsImo4DP4DYACfY2kL
Otkysmr3Dgsg9gIEtgXp2nQ=
=tYVb
-----END PGP SIGNATURE-----