User input filter

I've done this before but I cannot remember how or where I did it....
nopCommerce 4.20

I want to examine all user input and scan it for certain characters or character combinations. I have forgotten which piece of code that I used to parse through the user input looking for stuff.

Thanks much!

PS: advanced c# developer

Are you looking for validation?

Have a look at Nop.Web.Framework/Validators

Yes, that's sort of what I want. I want to examine all user input from any page and check it for opening and closing script tags. I'm working with an extremely anal pci compliance scanner who says that they are able to submit a script from user input. I know for a fact that is categorically not true. But, they fail me none the less. What I ended up doing was parking a filter on all user input and scanned for script tags. With that, I passed.