Hello,

I have a field that was once a required field.  I eventually decided not to
make it required (to make a long story short).  This is what I would like to
do instead:

We have a checkbox on our Main form labelled "Completed".  We check this
checkbox when a job has been completed, to release it from the work to be
done list.

I'd like to code the onClick event of the Completed checkbox so that a field
on my Documents subform, called "Document number", is looked at.  If the
value of the Document Number field is null, a warning message should pop up
saying "Document number cannot be left blank".  Once this field is filled in
(or if it's already filled in), the user is then allowed to check the
Completed checkbox.

How would for this be written?

Many thanks,