dita message

Subject: Non-breaking space in DITA?

From: "Yas Etessam" <yas.etessam@justsystems.com>
To: <dita@lists.oasis-open.org>
Date: Thu, 4 Oct 2007 16:56:47 -0700

Can anybody explain why the topic.mod file defines the non-breaking
space entity?

<!ENTITY nbsp                   "&#160;"                             >

None of the other character entity references for ISO 8859-1 have been
defined in the DITA DTDs.

Is this a special case? 

Best regards,

Yas Etessam