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

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

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