htslib tbx_conf_t: the column layout and parsing rules used to derive each
line’s index interval. The four named presets are the upstream constants
(tbx_conf_gff/bed/sam/vcf in tbx.c); a custom layout via -s/-b/-e is the
TBX_GENERIC path.
Print every record overlapping any of regions to out, in the order htslib
tabix emits them (region order; sorted within a region by file offset). The
column layout comes from the index header, so this works regardless of which
tool built the index.