Is fid beginning with a number valid in WFS?

[Rahkonen Jukka]

Hi,
 
I am trying to serve the same data through Mapserver WFS and Geoserver WFS.  Both are making GML packege when GetFeature is requested, but my WFS client accepts only the on sent by Geoserver.  Only real difference I can see is in fid.  While Geoserver always inserts something in the beginning of the fid to be sure that is does not start with number character, Mapserver does not. I wonder if fid starting with a number is valid according to WFS standard or not.  
 
Mapserver:
<gml:featureMember>
 <ms:roads fid="71">
 
Geoserver:
<gml:featureMember>
 <lv:towns fid="roads.71">
 
Regards,
 
-Jukka Rahkonen-