declaration/definition
declare markup-identification (#base | #full)
Use the markup-identification declaration to change the default interpretation of element names in element rule headers, and element context inquiries. The default interpretation is #full. A markup-identification declaration can specify either #full or #base.
A markup-identification declaration affects element names which follow, up to the next markup-identification declaration, or to the end of the program.
#xmlns is not a legal value, because element names in element rule headers may not be prefixed by #xmlns.
declare markup-identification #base
element x
do when parent of ancestor z is foo
...
done
is equivalent to:
element #base x
do when parent of ancestor #base z is #base foo
...
done