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PHP Manual

# Stream Contexts

A context is a set of parameters and wrapper specific options which modify or enhance the behavior of a stream. Contexts are created using stream_context_create() and can be passed to most filesystem related stream creation functions (i.e. fopen(), file(), file_get_contents(), etc...).

Options can be specified when calling stream_context_create(), or later using stream_context_set_option(). A list of wrapper specific options can be found in the Context options and parameters chapter.

Parameters can be specified for contexts using the stream_context_set_params() function.

Stream Filters
Stream Errors
Streams
PHP Manual