Local entities in XHTML

From: Yves MARCOUX <Yves.MARCOUX@UMontreal.CA> Date: Fri, 07 Dec 2007 12:11:39 -0500 Message-Id: <200712071711.lB7HBsdS026942@pruche.dit.umontreal.ca> To: www-html@w3.org · This archive was generated by hypermail 2.2.0+W3C-0.50 : Tuesday, 27 March 2012 18:16:13 GMT

Is it valid to include a local declaration subset in the DOCTYPE 
declaration of a XHTML document (e.g., for declaring an entity)? For example:

<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
   "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"
[
<!ENTITY ti "Nice title!">
]
 >
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
	 <title>&ti;</title>
</head>
....

The online W3C validator understands and accepts it, but no browser 
interprets it correctly.

Who is right??

Thank you!

Yves Marcoux