WordPress at a glance
filter is not described

request filter-hook . WP 2.1.0

Filters the array of parsed query variables.

Usage

add_filter( 'request', 'filter_function_name_1269' );
function filter_function_name_1269( $query_vars ){
	// filter...

	return $query_vars;
}
$query_vars(array)
The array of requested query variables.

Where the hook is called

WP::parse_request()
request
wp-includes/class-wp.php 366
$this->query_vars = apply_filters( 'request', $this->query_vars );

Where the hook is used (in WP core)

wp-includes/default-filters.php 467
add_filter( 'request', '_post_format_request' );