<REXX>
tag reference
in your HEAD block. You can then use
the following construct within any other tag within the BODY block:
<ANYTAG NAME="=("MyREXXCode att_param")" ...> ... =("MyREXXCode other_param") ... </ANYTAG>which would be translated before it is interpreted into:
<ANYTAG NAME="ABCatt_paramXYZ" ...> ... ABCother_paramXYZ ... </ANYTAG>which doesn't make much sense, but it shows how it works in principle.
See "Sample script with REXX"
for a more meaningful example.