The definition is that intervals are zero based and half-open. So by default the line "chrA lo hi" is parsed to the interval [lo + 1,
hi] on chromosome chrA. Similarly, when printing, the default is to print [lo - 1, hi]. The optional argument increment_lo_hi allows changing this behavior for non-conformant files. In addition, the optional argument chr_map is a string
-> string function that allows changing of the chromosome name to a specified format, and defaults to identity.
Some tools require that the set of intervals do not overlap within each chromosome. This is not enforced, but you can use any_overlap to verify this property when needed.