Character span (after the leading prefix — base; see formulaPrefixLen) of the reference at
refIndex — start = its first token's start, end = its last token's end. null if that reference
isn't present. Walks the ORIGINAL tokens (faithful text); used to tell whether the caret is on a
reference the picker rewrote, and to park it at that reference's end.
Character span (after the leading prefix —
base; see formulaPrefixLen) of the reference atrefIndex—start= its first token's start,end= its last token's end.nullif that reference isn't present. Walks the ORIGINAL tokens (faithfultext); used to tell whether the caret is on a reference the picker rewrote, and to park it at that reference's end.