SOLVED Tag: sinkhole (sink, swallow hole, shakehole, swallet, doline)

I am mapping a river which runs over karst, a Swiss-cheese-like rock structure full of holes, depressions, caverns and grottos (see As with many/most rivers that run over karst "my"river suddenly disappears into a sinkhole (see and then reappears, maybe a few hundred metres away, gushing out of another sinkhole (fluorescein-tracing of the water shows that it is the same river). Since, for the observer on the surface, the underground river is invisible I’d like to mark the points at which the river “disappears” and then “reappears” with a tag “sinkhole”.

I can’t find such a tag. Am I allowed to invent one ? [UPDATE: have finally found the tag at [url][/url] so this thread could be deleted if the moderator thinks fit]

P.S. I see that there is a related discussion in German at [url][/url] without a solution.