Feeling a bit dumb - tagging case insensitive regex

System

TS 6.7.2 SP3

I'm trying to get a validation regex working with case insensitivity.

Here is how it looks at the moment:

[HTML][/HTML]

I've unsuccessfully tried:

"/blah/i"
"(blah)i"

and more that I've forgotten by now. I can't seem to get any sort of case insensitivity working (other than

[eE][xX] .etc

which is just too tedious for me).

Am I missing something obvious here?

Thanks for anything.

Craig