Custom block page with ASM

Hi,

 

I'm fairly new to the ASM and have very little experience with iRules (which I have a feeling will be the only way to accomplish what I want.)

 

Basically, I'd like to know if there's a way to insert the reason for a block in the block response page. Something like Illegal character, or whatever. The reason being is that I have large forms that are being filled out by users, there's currently little to no client side validation, and if a user accidentally enters a wrong character, they will have no idea what it was and how to fix it.

 

So are there any ways to do this, or other variables that can be used other than <%TS.request.ID()%> ?

 

I'm on 11.2, FYI.

 

Thanks!