SPDX and docbook documentation, how to do properly?

[Friedrich W. H. Kossebau]

Hi,

the section "License Statements in Non-Source-Code Files" at
    https://community.kde.org/Guidelines_and_HOWTOs/
Licensing#License_Statements_in_Non-Source-Code_Files 
currently does not hold an example how to add SPDX tags. And by a quick look 
it seems not many docbook files in KDE repos currently have any such info, so 
no pattern could be derived from the real world samples.

Also unclear to me how to best integrate with the predefined docbook tags, or 
if duplication is needed?

Could we have some example given by those with insights?

Cheers
Friedrich