BUR #16955 has been approved by @nonamethanks.
create alias sitting_on_railing -> on_railing
create implication on_railing -> railing
two tags with similar usage, only that on railing can be used beyond sitting, such as standing or resting on it. the implication should be self-explanatory, if I ever see some non-euclidean rail standing without a railing I will delete my account.
note: there are a decent amount of against railing mistags in here, but that isn't really a fault of the tag. I'll go through and fix them later, don't let it stop the BUR.