The Invisible Pink Unicorn.
An SEP-field is an easy way to make things invisible.

This is a quick hack to hide field content only on the desktop client.

Put fields you don’t want to see on the desktop into {{sep:NN}} templates, and they become somebody else’s problem.

On AnkiWeb and AnkiDroid (and AnkiMobile), the template is unknown and default behavior is to show the text without modification – the field becomes visible again.

This is only needed for audio/video files. Text or images can be hidden with clever CSS:

<span class="justdt">Shown on desktop</span>
<span class="justmobile">Shown on mobile</span>

in the card template and

.justmobile {display:none;}
.mobile .justmobile {display:inline;}
.mobile .justdt {display:none;}

in the card CSS.

The problem was that i didn’t want to copy a bunch of video files to my Android device to save FAT directory entries, which are in short supply if you have a collection with many files with long names.