DOCBOOK: example of Element <tgroup> with it's attribute cols .

Hi anyone with an example of Element <tgroup> with it's attribute cols .

I am trying to get the columns to work without Elements  </row> & </entry>

Don't understand how to invoke NMTOKEN datatype as it's#REQURIED for 
Element </tgroup>

Please point or illustrate Cheers all.

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Regards 
Chuck Amadi
ICT Dept Systems Programmer
Rhaglenydd Systemau Adran ICT