I have some limited understanding of the use of the equal sign in the property sheet. For instance, I know how to create a mult-line caption by setting the caption property to

='abc'+chr(13)+'def'

Now, I've never seen any documentation on this feature, so I have a few questions. What are the limitations on what I put after the equal sign? When is it evaluated? Which of the following, if any, make sense?

=m.SomeVariable
=clr_Purple && where clr_Purple is #defined in an include file
=SomeUDF(...)

Thanks in advance,