$offset
$offset : int
A byte range for a partial read.
Reading one frame out of a 1 MiB pack is the common case; without a range the whole pack comes down to serve a few kilobytes.
__construct(int $offset, int $length) : mixed
Constructs a range.
| int | $offset | First byte to read, counting from zero. |
| int | $length | How many bytes to read. |
When the offset is negative or the length is not positive. A zero-length range is refused rather than returning an empty string, since it is always a caller bug.