SPARQL variable names syntax

Dear RDF Data Access Working Group Members,

In the last working draft of the 21st. of July 2005, changes have been done
concerning the definition of the variable names within a SPARQL query.
The syntax is specified under 
http://www.w3.org/TR/rdf-sparql-query/#rVARNAME .
I'm wondering if there is any reason not to allow the underscore "_" at the
Beginning of a variable name from the grammar point of view.
This could be very useful for application that build SPARQL queries
automatically and call the variables like the RDF:ID of the searched
resource.

Let's suppose we have the following data
<http://example.org/book1> <http://properties.com/_title> "SPARQL Tutorial".

A Generated query could look like:

PREFIX  exp: <http://example.org/>
PREFIX  pro: <http://properties.com/>
SELECT  $_title
WHERE   { exp:book1  pro:_title  $title }

In general, SPARQL based application developers should not care about
calling the variables. It should be possible to just take over the RDF
Property ID with a "?" as a prefix. Thus, I think that, the syntax of NCNAME
http://www.w3.org/TR/rdf-sparql-query/rNCNAME should be equal to that of
variable names.

I would be very glad and thankful for your considerations and for any
explanations or remarks.

Best Regards
--------------------------
Walid Maalej
Technical University of Munich
Web:    www.in.tum.de