current position (seek with SEEK_CUR, not SEEK_SET). Only positive values are
allowed. This breaking change is necessary to fix the erratic behavior in
streams without a seek handlder. Addresses bug #53006.
#Note that the example on the doc page for stream_get_contents() may fail
#without this change.
#This change is also in the spirit of stream_get_contents(), whose description
#is "Reads all remaining bytes (or up to maxlen bytes) from a stream...".
#Previous behavior allowed setting the file pointer to positions before the
#current one, so they wouldn't be "remaining bytes". The previous behavior was
#also inconsistent in that it allowed an moving to offset 1, 2, ..., but not 0.
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