Substitution rules CO prerequisite

Hi all,

Do you know how can I use field "Storage location" LGORT in the prerequisite of substitution rule for controlling.

This field is not in the structure COBL. It is in structure VBAP, but somehow my subst. rule is not working when I put in the prerequisite VBAP-LGORT.

Do you had similar issues? What can be done to use storage location in the prerequisite?

Do you have any documentation about the usage of substitution rules?

Thanks,

Maria