integer value float value
key: numeric tag id, the corresponding string is bcf_hdr_t::idBCF_DT_ID[$key].key
vptr offset, i.e., the size of the INFO key plus size+type bytes indicates that vptr-vptr_off must be freed; set only when modified and the new data block is bigger than the original +//// vector length, 1 for scalar
type: one of BCF_BT_* types
only set if $len==1; for easier access
pointer to data array in bcf1_t->shared.s, excluding the size+type and tag id bytes
INFO field data (§1.4.1 Fixed fields, (8) INFO)