Index: src/wp-admin/includes/class-wp-press-this.php
===================================================================
--- src/wp-admin/includes/class-wp-press-this.php	(revision 33062)
+++ src/wp-admin/includes/class-wp-press-this.php	(working copy)
@@ -390,93 +390,93 @@ class WP_Press_This {
 	/**
 	 * Utility method to limit image source URLs.
 	 *
 	 * Excluded URLs include share-this type buttons, loaders, spinners, spacers, WP interface images,
 	 * tiny buttons or thumbs, mathtag.com or quantserve.com images, or the WP stats gif.
 	 *
 	 * @ignore
 	 * @since 4.2.0
 	 *
 	 * @param string $src Image source URL.
 	 * @return string If not matched an excluded URL type, the original URL, empty string otherwise.
 	 */
 	private function _limit_img( $src ) {
 		$src = $this->_limit_url( $src );
 
-		if ( preg_match( '/\/ad[sx]{1}?\//', $src ) ) {
+		if ( preg_match( '!/ad[sx]?/!i', $src ) ) {
 			// Ads
 			return '';
-		} else if ( preg_match( '/(\/share-?this[^\.]+?\.[a-z0-9]{3,4})(\?.*)?$/', $src ) ) {
+		} else if ( preg_match( '!(/share-?this[^.]+?\.[a-z0-9]{3,4})(\?.*)?$!i', $src ) ) {
 			// Share-this type button
 			return '';
-		} else if ( preg_match( '/\/(spinner|loading|spacer|blank|rss)\.(gif|jpg|png)/', $src ) ) {
+		} else if ( preg_match( '!/(spinner|loading|spacer|blank|rss)\.(gif|jpg|png)!i', $src ) ) {
 			// Loaders, spinners, spacers
 			return '';
-		} else if ( preg_match( '/\/([^\.\/]+[-_]{1})?(spinner|loading|spacer|blank)s?([-_]{1}[^\.\/]+)?\.[a-z0-9]{3,4}/', $src ) ) {
+		} else if ( preg_match( '!/([^./]+[-_])?(spinner|loading|spacer|blank)s?([-_][^./]+)?\.[a-z0-9]{3,4}!i', $src ) ) {
 			// Fancy loaders, spinners, spacers
 			return '';
-		} else if ( preg_match( '/([^\.\/]+[-_]{1})?thumb[^.]*\.(gif|jpg|png)$/', $src ) ) {
+		} else if ( preg_match( '!([^./]+[-_])?thumb[^.]*\.(gif|jpg|png)$!i', $src ) ) {
 			// Thumbnails, too small, usually irrelevant to context
 			return '';
-		} else if ( preg_match( '/\/wp-includes\//', $src ) ) {
+		} else if ( preg_match( '!/wp-includes/!', $src ) ) {
 			// Classic WP interface images
 			return '';
-		} else if ( preg_match( '/[^\d]{1}\d{1,2}x\d+\.(gif|jpg|png)$/', $src ) ) {
+		} else if ( preg_match( '![^\d]\d{1,2}x\d+\.(gif|jpg|png)$!i', $src ) ) {
 			// Most often tiny buttons/thumbs (< 100px wide)
 			return '';
-		} else if ( preg_match( '/\/pixel\.(mathtag|quantserve)\.com/', $src ) ) {
+		} else if ( preg_match( '!/pixel\.(mathtag|quantserve)\.com!i', $src ) ) {
 			// See mathtag.com and https://www.quantcast.com/how-we-do-it/iab-standard-measurement/how-we-collect-data/
 			return '';
-		} else if ( preg_match( '/\/[gb]\.gif(\?.+)?$/', $src ) ) {
+		} else if ( preg_match( '!/[gb]\.gif(\?.+)?$!i', $src ) ) {
 			// Classic WP stats gif
 			return '';
 		}
 
 		return $src;
 	}
 
 	/**
 	 * Limit embed source URLs to specific providers.
 	 *
 	 * Not all core oEmbed providers are supported. Supported providers include YouTube, Vimeo,
 	 * Vine, Daily Motion, SoundCloud, and Twitter.
 	 *
 	 * @ignore
 	 * @since 4.2.0
 	 *
 	 * @param string $src Embed source URL.
 	 * @return string If not from a supported provider, an empty string. Otherwise, a reformattd embed URL.
 	 */
 	private function _limit_embed( $src ) {
 		$src = $this->_limit_url( $src );
 
 		if ( empty( $src ) )
 			return '';
 
-		if ( preg_match( '/\/\/(m|www)\.youtube\.com\/(embed|v)\/([^\?]+)\?.+$/', $src, $src_matches ) ) {
+		if ( preg_match( '!//(m|www)\.youtube\.com/(embed|v)/([^?]+)\?.+$!i', $src, $src_matches ) ) {
 			// Embedded Youtube videos (www or mobile)
 			$src = 'https://www.youtube.com/watch?v=' . $src_matches[3];
-		} else if ( preg_match( '/\/\/player\.vimeo\.com\/video\/([\d]+)([\?\/]{1}.*)?$/', $src, $src_matches ) ) {
+		} else if ( preg_match( '!//player\.vimeo\.com/video/([\d]+)([?/].*)?$!i', $src, $src_matches ) ) {
 			// Embedded Vimeo iframe videos
 			$src = 'https://vimeo.com/' . (int) $src_matches[1];
-		} else if ( preg_match( '/\/\/vimeo\.com\/moogaloop\.swf\?clip_id=([\d]+)$/', $src, $src_matches ) ) {
+		} else if ( preg_match( '!//vimeo\.com/moogaloop\.swf\?clip_id=([\d]+)$!i', $src, $src_matches ) ) {
 			// Embedded Vimeo Flash videos
 			$src = 'https://vimeo.com/' . (int) $src_matches[1];
-		} else if ( preg_match( '/\/\/vine\.co\/v\/([^\/]+)\/embed/', $src, $src_matches ) ) {
+		} else if ( preg_match( '!//vine\.co/v/([^/]+)/embed!i', $src, $src_matches ) ) {
 			// Embedded Vine videos
 			$src = 'https://vine.co/v/' . $src_matches[1];
-		} else if ( preg_match( '/\/\/(www\.)?dailymotion\.com\/embed\/video\/([^\/\?]+)([\/\?]{1}.+)?/', $src, $src_matches ) ) {
+		} else if ( preg_match( '!//(www\.)?dailymotion\.com/embed/video/([^/?]+)([/?].+)?!i', $src, $src_matches ) ) {
 			// Embedded Daily Motion videos
 			$src = 'https://www.dailymotion.com/video/' . $src_matches[2];
 		} else {
 			require_once( ABSPATH . WPINC . '/class-oembed.php' );
 			$oembed = _wp_oembed_get_object();
 
 			if ( ! $oembed->get_provider( $src, array( 'discover' => false ) ) ) {
 				$src = '';
 			}
 		}
 
 		return $src;
 	}
 
 	/**