Runtime Configuration

The behaviour of these functions is affected by settings in php.ini.

Output Control configuration options

Name	Default	Changeable	Changelog
output_buffering	"0"	PHP_INI_PERDIR
output_handler	NULL	PHP_INI_PERDIR	Available since PHP 4.0.4.
implicit_flush	"0"	PHP_INI_ALL	PHP_INI_PERDIR in PHP <= 4.2.3.
url_rewriter.tags	"a=href,area=href,frame=src,form=,fieldset="	PHP_INI_ALL	Available since PHP 4.0.4. Before PHP 7.1.0, this was used to set session's trans sid rewrite. From PHP 7.1.0, it is only used by output_add_rewrite_var.
url_rewriter.hosts	$_SERVER['HTTP_HOST'] is used as default.	PHP_INI_ALL	Available since PHP 7.1.0

For further details and definitions of the PHP_INI_* modes, see the Where a configuration setting may be set.

Here's a short explanation of the configuration directives.

output_buffering boolean/integer

You can enable output buffering for all files by setting this directive to 'On'. If you wish to limit the size of the buffer to a certain size - you can use a maximum number of bytes instead of 'On', as a value for this directive (e.g., output_buffering=4096). This directive is always Off in PHP-CLI.

output_handler string

You can redirect all of the output of your scripts to a function. For example, if you set output_handler to mb_output_handler, character encoding will be transparently converted to the specified encoding. Setting any output handler automatically turns on output buffering.

Note:

You cannot use both mb_output_handler with ob_iconv_handler and you cannot use both ob_gzhandler and zlib.output_compression.

Note:

Only built-in functions can be used with this directive. For user defined functions, use ob_start.

implicit_flush boolean

FALSE by default. Changing this to TRUE tells PHP to tell the output layer to flush itself automatically after every output block. This is equivalent to calling the PHP function flush after each and every call to print or echo and each and every HTML block.

When using PHP within an web environment, turning this option on has serious performance implications and is generally recommended for debugging purposes only. This value defaults to TRUE when operating under the CLI SAPI.

See also ob_implicit_flush.

url_rewriter.tags string

url_rewriter.tags specifies which HTML tags are rewritten by output_add_rewrite_var values. Defaults to a=href,area=href,frame=src,input=src,form= form is special tag. <input hidden="session_id" name="session_name"> is added as form variable.

Note: Before PHP 7.1.0, url_rewriter.tags was used to specify session.trans_sid_tags. Since PHP 7.1.0, fieldset is no longer considered as special tag.

url_rewriter.hosts string

url_rewriter.hosts specifies which hosts are rewritten to include output_add_rewrite_var values. Defaults to $_SERVER['HTTP_HOST']. Multiple hosts can be specified by ",", no space is allowed between hosts. e.g. php.net,wiki.php.net,bugs.php.net