Dear contexers,
I get the impression that cals tables need to be processed separately from the main docbook file.
Instead of <table> and <tbody>, etc. the tags are changed into <cals:table>, <cals:tbody>, etc.
I first tried to process the file x-cals-test.tex pointed to by Hans.
This file loads two other files
\starttext
\xmlloaddirectives{x-cals-test.cdx}
\xmlprocess{main}{x-cals-test.xml}{}
\stoptext
However, the file x-cals-test.xml is not valid.
Therefore I took one of the simple cals tables from within that file, making sure it contains one of the cdx attributes (cdx="vertical") and saved it in x-cals-test2.xml. My xml software says that the file is valid, and it opens normally.
The file are processed now, but the table is not typeset.
Instead there is an error message printed in the pdf file: invalid xml file - parsed text.
The log file says: lxml : no directives found in 'x-cals-test.cdx' (more log information further)
It seems that the directives are not processed.