ReadonlyfeaturesTOTAL number of features this query matched, unaffected by
limit/offset -- it is the size of the answer, not of the page you are
about to iterate. For a filtered query it is the post-filtered match
count, never the candidate count. undefined means the file declares an
unknown feature count (a stored 0) and the query did not go through an
index, so no total is knowable without a full scan.
A cursor over features.
featuresCountisundefinedwhen the header does not know it: the format writes 0 for UNKNOWN, not for empty, so it must never be reported as a count of zero.