In most of these lines it is doing its ordinary job of marking where or when something is — next to the members, in the UK, at this very moment, one out of the two. Two lines show the thing this entry is named for: in casual speech people slot it in where writing would use 의, so 'the special thing about Daehak-ro performances' and 'the front part of this sentence' both use 에. That habit is real, but two lines are not enough to describe its range, so this entry is only partial.
The examples below did not fully pin this one down — read them before relying on the entry above.