Report Server: Show/hide textbox by an expression

Today I was struggling with hiding a textbox on a report (in Report Builder) by using an expression. I tried to evaluate the number of subfunctions of a certain person. The evaluation worked, but the textbox didn't show up when 1 or more subfunctions were available.
The expression was:

=IIf((Count(Fields!Uid.Value, "dsSubFunctions")<1),False,True)

WRONG! The property you will set is named 'Hidden', so it's just the other way around:

=IIf((Count(Fields!Uid.Value, "dsSubFunctions")<1),True,False)

And stupid of me, it is just written right above the expression-textbox: 'Set the expression for: Hidden'

Anyway, just thought to share it, in case there are some more (lazy) programmers who don't read every single line of text Microsoft shows you :)