DTD customization throwing error while checkIn

Hello team,

I have customized DTD file to accept ish-variables-atts in mainbooktitle. But while checkIn the bookmap, i am getting an error "varref" attribute is not declared. Below is my code

1. Added the entity "ish-variables-atts" in bookmap.mod

<!ENTITY % ish-variables-atts
           "ishvarinusexpath    CDATA #FIXED    './@varref'
            ishvarassignedxpath CDATA #FIXED    './@varid'
            varref              CDATA #IMPLIED
            varid               CDATA #IMPLIED">

2. Called the entity in the mainbooktitle.attributes

<!ENTITY % mainbooktitle.attributes
             "keyref
                        CDATA
                                  #IMPLIED
              %univ-atts;
              %ishlabelxpath-general-default;
              %ishlinkxpath-general-default;
              %ish-variables-atts;
              outputclass
                        CDATA
                                  #IMPLIED"
>

Document is valid in XMetal, while check in the document to SDL i am getting the "varref" not declcared error.

Anyone can tell me what I am missing here?

Thanks

Roopesh Navath