x1 (proposition) is a clause expressing adverbial relation x2 (property of nonce place, has places for ce'u referring to members of x3) and connecting members of x3 (ordered group)
The first member of x3 is what follows after the adposition expressing adverbial relation x2. The second member of x3 can sometimes be called 'noun phrase of adposition'; it can e.g. be the current clause (lo bridi), x1 of it, x2 of it etc. See also bridi, sumti, sumtcita.