Source

File: wp-includes/formatting.php

function convert_chars( $content, $deprecated = '' ) {
	if ( ! empty( $deprecated ) ) {
		_deprecated_argument( __FUNCTION__, '0.71' );
	}

	if ( strpos( $content, '&' ) !== false ) {
		$content = preg_replace( '/&([^#])(?![a-z1-4]{1,8};)/i', '&$1', $content );
	}

	return $content;
}