MIME Types to exclude

Under Custom/Resident Task Settings/Exceptions, there are 5 types listed to exclude. Why are they excluded? I tried to delete them, but they came back. The types are: audio/, image/gif, image/png, text/css, video/

As far I know, they’re there, into WebShield exceptions, due to the way WebShield scans the http traffic and the way of that files are transmitted. They’re safe to be excluded. Anyway, a more knowledge one should give the final answer.
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