Hi:

 

The problem is that the Editor use browser's editing service , and the browser do not understand your <flashvideo> tag and would not display it .

 

And the CSS is not able to affect the unknown tag too.

 

So the Editor6.x would not support selecting the unknown tag now.

 

By the way ,

We are considering new rendering method of the CuteEditor7 and it would support the custom tags.

 

Regards , Terry .