Source

File: wp-includes/formatting.php

function sanitize_title_with_dashes( $title, $raw_title = '', $context = 'display' ) {
	$title = strip_tags( $title );
	// Preserve escaped octets.
	$title = preg_replace( '|%([a-fA-F0-9][a-fA-F0-9])|', '---$1---', $title );
	// Remove percent signs that are not part of an octet.
	$title = str_replace( '%', '', $title );
	// Restore octets.
	$title = preg_replace( '|---([a-fA-F0-9][a-fA-F0-9])---|', '%$1', $title );

	if ( seems_utf8( $title ) ) {
		if ( function_exists( 'mb_strtolower' ) ) {
			$title = mb_strtolower( $title, 'UTF-8' );
		}
		$title = utf8_uri_encode( $title, 200 );
	}

	$title = strtolower( $title );

	if ( 'save' === $context ) {
		// Convert &nbsp, &ndash, and &mdash to hyphens.
		$title = str_replace( array( '%c2%a0', '%e2%80%93', '%e2%80%94' ), '-', $title );
		// Convert &nbsp, &ndash, and &mdash HTML entities to hyphens.
		$title = str_replace( array( ' ', ' ', '–', '–', '—', '—' ), '-', $title );
		// Convert forward slash to hyphen.
		$title = str_replace( '/', '-', $title );

		// Strip these characters entirely.
		$title = str_replace(
			array(
				// Soft hyphens.
				'%c2%ad',
				// &iexcl and &iquest.
				'%c2%a1',
				'%c2%bf',
				// Angle quotes.
				'%c2%ab',
				'%c2%bb',
				'%e2%80%b9',
				'%e2%80%ba',
				// Curly quotes.
				'%e2%80%98',
				'%e2%80%99',
				'%e2%80%9c',
				'%e2%80%9d',
				'%e2%80%9a',
				'%e2%80%9b',
				'%e2%80%9e',
				'%e2%80%9f',
				// Bullet.
				'%e2%80%a2',
				// &copy, &reg, &deg, &hellip, and &trade.
				'%c2%a9',
				'%c2%ae',
				'%c2%b0',
				'%e2%80%a6',
				'%e2%84%a2',
				// Acute accents.
				'%c2%b4',
				'%cb%8a',
				'%cc%81',
				'%cd%81',
				// Grave accent, macron, caron.
				'%cc%80',
				'%cc%84',
				'%cc%8c',
			),
			'',
			$title
		);

		// Convert &times to 'x'.
		$title = str_replace( '%c3%97', 'x', $title );
	}

	// Kill entities.
	$title = preg_replace( '/&.+?;/', '', $title );
	$title = str_replace( '.', '-', $title );

	$title = preg_replace( '/[^%a-z0-9 _-]/', '', $title );
	$title = preg_replace( '/\s+/', '-', $title );
	$title = preg_replace( '|-+|', '-', $title );
	$title = trim( $title, '-' );

	return $title;
}