The comma sits at the baseline, so between two raised digits it drops away from
them and reads as a stray mark on the line. A space separates them without
introducing a character that lives at the wrong height.
[1][2] and [1, 2] both still arrive as two raised digits, still in the order the
model wrote them, and a run containing a number we were never shown is still
left exactly as written.
adrianbonpin