The input was pure ASCII, so an analyzed-byte offset into it is also a JS
string index — the test a caller needs before it may treat the spans above
as offsets into original itself. Published from the coordinate pass this
result already ran rather than re-derived, so the two cannot disagree.
comment spans (analyzed-byte offsets), dropped from the statement stream.
Unbalanced delimiters and other structural surprises, each located; never
a throw. Includes the two coordinate-pass classes (bom, non-ascii).
The full segmentation of one input string.