_canonical_charset() │ WP 3.6.0

Retrieves a canonical form of the provided charset appropriate for passing to PHP functions such as htmlspecialchars() and charset HTML attributes.

Internal function — this function is designed to be used by the kernel itself. It is not recommended to use this function in your code.

No Hooks.

Returns

String. The canonical form of the charset.

Usage

_canonical_charset( $charset );
$charset(string) (required)
A charset name, e.g. "UTF-8", "Windows-1252", "SJIS".

Notes

Changelog

Since 3.6.0 Introduced.

_canonical_charset() code WP 6.8.1

wp-includes/functions.php 
function _canonical_charset( $charset ) {
	if ( is_utf8_charset( $charset ) ) {
		return 'UTF-8';
	}

	/*
	 * Normalize the ISO-8859-1 family of languages.
	 *
	 * This is not required for htmlspecialchars(), as it properly recognizes all of
	 * the input character sets that here are transformed into "ISO-8859-1".
	 *
	 * @todo Should this entire check be removed since it's not required for the stated purpose?
	 * @todo Should WordPress transform other potential charset equivalents, such as "latin1"?
	 */
	if (
		( 0 === strcasecmp( 'iso-8859-1', $charset ) ) ||
		( 0 === strcasecmp( 'iso8859-1', $charset ) )
	) {
		return 'ISO-8859-1';
	}

	return $charset;
}