display:none in internal css stylesheet

Hi,

I have a simple question. Does the FCK Editor(Version 2.6.5) internal css stylesheet, which contains a display:none statement for a non-standard-html Tag (<xy>zzz</xy>), work using IE 7 Browser ?
I my experience it does not, but other statements like text-decoration:line-through; work fine.

Thanks.

With greetings
halmarius