Stream::expression & case insenitivity

I am trying to create a bit of a badword list and as a test intend to use this iRule. It works fine but I'm struggling to add case insensitivity to the mix. I've tried wrapping [string tolower] round it with no success and have read I may need to use a regex but wonder if there is a better way.

Any suggestions much appreciated.

Thanks.

when HTTP_RESPONSE {

HTTP::header remove server

foreach header {Server Date X-Powered-By} {

while { [HTTP::header exists $header] } {

log local0. "Removing- $header: [HTTP::header value $header]"

HTTP::header remove $header

}

}

Disable the stream filter by default

STREAM::disable

Check if response type is text

if {[HTTP::header value Content-Type] contains "text"}{

Replace content in STREAM expression

STREAM::expression "@badword@*****@ @badword2@*****@ @badword3@*****@" ]

Enable the stream filter for this response only

STREAM::enable

}

}