stream_copy_to_stream() treats $offset of 0 as "current position"

Documentation does not mention that $offset of 0 keeps $from's position rather than copying from 0th offset.

<?php
$a = fopen('php://memory', 'r+');
$b = fopen('php://memory', 'r+');
fwrite($a, '0123456789');
fseek($a, 3);
stream_copy_to_stream($a, $b, 2, 0);
rewind($b);
echo stream_get_contents($b);

This code outputs 34 and not 01 as suggested by the documentation.

To me, this looks more like an implementation issue because $offset may depend on external factors such as user's input, and code most often doesn't expect the function's seeking behaviour to change if the input is zero or non-zero.

Related code (note the pos > 0 condition):

https://github.com/php/php-src/blob/11b612af6dbe9fdd60edb58d37e441c97bff79e0/ext/standard/streamsfuncs.c#L481-L509

PHP_FUNCTION(stream_copy_to_stream)
{
	// ...
	if (pos > 0 && php_stream_seek(src, pos, SEEK_SET) < 0) {

Start with the stream_copy_to_stream() documentation and compare its $offset wording with ext/standard/streamsfuncs.c around the linked lines, especially the pos > 0 condition. Run the provided PHP example to confirm the behavior; done means the documentation accurately describes zero-offset behavior, or the issue is routed to the implementation if that behavior is unintended.