You can use this option in link descriptions and compilation descriptions.
You use this option to define a logical dependency between targets and/or files.
Translating module file X results in the by-product Y. You can use this option to specify that X should be retranslated as soon as Y no longer exists or is obsolete and therefore has to be recreated.
vco01.idl extdep=$WRK/incl/livecache.h