（在）…（之）中grammar point · tier 2 · among … (在)…(之)中 — pick one out of a bounded set
Fences a named set as the range, then singles out one member from inside it: (在) [set] (之)中 = among [set], [this one].
字源 FORM what the parts do
在 sets you down inside: 土 holds the ground, 才 gives the sound. 中 is a pole driven through a bounded space — the inside of it. The set fills the gap between them, and an optional 之 links the set to 中 the classical way. 在 puts you within the set; 中 walls the set shut; the standout member gets named after.
故事 STORY a scene to remember it by
A crowd is fenced into one yard; from inside that fence one figure steps forward and every eye turns to it.
字源自撰記憶法
框 · Frame
(在) [set noun] (之)中，[one member singled out]
觸 · Trigger
You have a whole set in view and you want to name it as the range, then pick out the one that stands out from inside it.
序 · The move
1Name the set inside the gap: a plural or many-membered group (各種美食, 這些人).Is it a set with members to choose among, not a single thing or a measured length?
2Wall it: close with 中, or 之中 for the more formal/written closing; front it with optional 在.Does 中 sit right after the set, with 之 only when the set links classically?
3Name the member that steps out, then comment on it.Is the comment about one member from inside the set, not about the whole set?
例 · Examples
1在臺灣各種gèzhǒng — every kind of, all sorts of美食měishí — fine food, delicacies中，他最喜歡zuì xǐhuān — likes the most小籠包。
Among Taiwan's many kinds of food, the one he likes best is xiaolongbao.
(在)…(之)中 names the set inline in the gap and picks the standout in one move (在各種美食中…); 其中 reaches BACK at a set already named in an earlier clause (…美食，其中…). 中 names then picks; 其中 points back, then picks.
…以內/之內 (within a span)
…(之)中 fences a set of members and singles one out from it; …以內/之內 caps a measured stretch of time or quantity and places an event somewhere inside the limit. Members to choose among vs a size not to exceed.
在…裡 (inside a container)
在…裡 is a physical room with walls (在盒子裡); 在…(之)中 fences an abstract set or range to pick a member from (在這些人中). Container vs the midst of a group.
✗ 在小籠包中，他最喜歡臺灣美食。 → ✓ 在臺灣美食中，他最喜歡小籠包。 (the set fills the gap and the standout comes after; don't fence one member and pick the whole set)
✗ 在這個人中，他最高。 → ✓ 在這些人中，他最高。 (中 needs a many-membered set to pick from, not a single person)
✗ 三天中做完 → ✓ 三天之內做完 (a measured stretch of time takes 之內, not the set-fencing 之中)
English 'among X' lets X be almost anything and floats freely in the clause; (在)…(之)中 wraps the set as a fronted range and 中 sits AFTER the set word, so the order reverses and the standout member follows the whole frame.