enable compression if parameter exists in content type

Newbie here. I'm trying to compress data with content type "text/html;charset=UTF-8". I do not want to compress the data if the parameter is missing i.e content type "text/html" should not be compressed but "text/html;charset=UTF-8" should.

 

 

I've tried using the following rule but without success.

 

 

when HTTP_RESPONSE {

 

set content_type [string tolower [HTTP::header Content-Type]]

 

if { $content_type contains "text/html;charset=UTF-8"}{

 

COMPRESS::enable

 

}

 

}