formatting.php

<?php
/**
 * Parses a string into variables to be stored in an array.
 *
 *
 * @param string $string The string to be parsed.
 * @param array $array Variables will be stored in this array.
 *
 * @since 2.2.1
 *
 */
function wp_parse_str( $string, &$array ) {

	if ( '' == $string ) {
		parse_str( $string, $array );
    /** This filter is documented below */
    $array = apply_filters( 'wp_parse_str', $array );

		return;
	}

	if ( null == $array ) {
		$array = array();
	}

	# split on outer delimiter
	$pairs = explode( '&', $string );

	# loop through each pair
	foreach ( (array) $pairs as $i ) {
		# split into name and value
		list( $name, $value ) = explode( '=', $i, 2 );

		# if name already exists
		if ( isset( $array[ $name ] ) ) {
			# stick multiple values into an array
			if ( is_array( $array[ $name ] ) ) {
				$array[ $name ][] = $value;
			} else {
				$array[ $name ] = array( $array[ $name ], $value );
			}
		} # otherwise, simply stick it in a scalar
		else {
			$array[ $name ] = $value;
		}
	}

	/**
	 * Filters the array of variables derived from a parsed string.
	 *
	 * @param array $array The array populated with variables.
	 *
	 * @since 2.3.0
	 *
	 */
	$array = apply_filters( 'wp_parse_str', $array );
}