"Extension is…" rules — multiple extensions?

Curious if we can add comma- or space-separated extensions in the "Extention is…" rules to catch multiple formats?
Specifically, I am looking to convert video files, but only those with the extension of .avi and .mkv and I need the rules criteria to be "match all", so I can't add two separate rules. I suppose I could have another rule which changes the color labels, but being able to add multiple extensions would be much easier.
I tried space-separated and comma-separated conditions, using both "is" and "contains", but neither seems to work.
Specifically, I am looking to convert video files, but only those with the extension of .avi and .mkv and I need the rules criteria to be "match all", so I can't add two separate rules. I suppose I could have another rule which changes the color labels, but being able to add multiple extensions would be much easier.
I tried space-separated and comma-separated conditions, using both "is" and "contains", but neither seems to work.