This is a regular stream implementation, possibly wrapper .
Streams were introduced with PHP 4.3.0 as a way to generalize a file, network, data compression, and other operations that share a common set of functions and applications. In its simplest definition, a stream is a resource object that exhibits stream behavior. That is, it can be read or written linearly and fseek () can use arbitrary locations in the stream.
Take a look at the calls to the stream_ family of functions and you will find where it was declared, and what exactly it does with the base file.
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