Syntax to create a Message popup

[SMO]

Wondering if anyone knows syntax that can be used in an expression that pulls up a message window when that expression meets a specific condition? Knowledge Fusion syntax I believe.

One example I've used this syntax for was with a conditional statement for a standard parts, Below which is to be used within some arc length range, per the manufacturer's specifications. Since the model was deformable by a Guide String, and I had no control over how a designer would create that guide sring, I opted to set the rule with, Suppression by Expression on the below geometry which would make the below disappear (suppress) if the user attempted deform along a Guide String that is too short or too long. However just making the below disappear without an explanation is confusing I added syntax in the conditional statement that 'basically' said:

if the deformation is < than this arc length and > that arc length, else suppress the geometry and launch message window. In this window popup, I was able to explain why the Below disappeared and also stated the manufacturers specifications.

I'd like to use this again but I cannot remember the syntax or where I found it originally.

Thanks,

Regards,
SMO (NX11)