XPath expression that generates false plus a message?

Hi Folks,

I want an XPath expression that is an if-then-else:

     If (condition) then
         true()
    else
        false()

If "condition" is satisfied then return true, else return false. However, in
addition to returning false, I want to return a message.

Here's an example that illustrates what I want to do:

----------------------------------------------------------------------
if (xs:time(start) gt xs:time(end)) then
     true()
else
     trace(false(), 'Hey, the meeting ends before it begins!')
----------------------------------------------------------------------

Unfortunately, that doesn't work. I guess the "else" part is actually
returning true.

If there any way to return a false, but have a string come along with it?

/Roger