(PHP 4 >= 4.0.4, PHP 5, PHP 7) ob_start callback function to gzip output buffer

(PHP 4 >= 4.3.0, PHP 5, PHP 7) Flush the output buffer, return it as a string and turn off output buffering

(PHP 4 >= 4.3.0, PHP 5, PHP 7) List all output handlers in use

(PHP 4 >= 4.3.0, PHP 5, PHP 7) Get current buffer contents and delete current output buffer

(PHP 4, PHP 5, PHP 7) Clean (erase) the output buffer and turn off output buffering

(PHP 4, PHP 5, PHP 7) Turn on output buffering

(PHP 4 >= 4.2.0, PHP 5, PHP 7) Return the nesting level of the output buffering mechanism