Index: src/wp-includes/class-wp-editor.php
===================================================================
--- src/wp-includes/class-wp-editor.php	(revision 29256)
+++ src/wp-includes/class-wp-editor.php	(working copy)
@@ -1375,7 +1375,7 @@
 		<?php wp_nonce_field( 'internal-linking', '_ajax_linking_nonce', false ); ?>
 		<div id="link-modal-title">
 			<?php _e( 'Insert/edit link' ) ?>
-			<div id="wp-link-close" tabindex="0"></div>
+			<button id="wp-link-close"><span class="screen-reader-text"><?php _e( 'Close' ); ?></span></button>
 	 	</div>
 		<div id="link-selector">
 			<div id="link-options">
@@ -1390,7 +1390,7 @@
 					<label><span>&nbsp;</span><input type="checkbox" id="link-target-checkbox" /> <?php _e( 'Open link in a new window/tab' ); ?></label>
 				</div>
 			</div>
-			<p class="howto" id="wp-link-search-toggle"><?php _e( 'Or link to existing content' ); ?></p>
+			<p class="howto"><a href="#" id="wp-link-search-toggle"><?php _e( 'Or link to existing content' ); ?></a></p>
 			<div id="search-panel">
 				<div class="link-search-wrapper">
 					<label>
@@ -1399,14 +1399,17 @@
 						<span class="spinner"></span>
 					</label>
 				</div>
-				<div id="search-results" class="query-results">
+				<div id="search-results" class="query-results" tabindex="0">
 					<ul></ul>
 					<div class="river-waiting">
 						<span class="spinner"></span>
 					</div>
 				</div>
-				<div id="most-recent-results" class="query-results">
-					<div class="query-notice"><em><?php _e( 'No search term specified. Showing recent items.' ); ?></em></div>
+				<div id="most-recent-results" class="query-results" tabindex="0">
+					<div class="query-notice" id="query-notice-message">
+						<em class="query-notice-default"><?php _e( 'No search term specified. Showing recent items.' ); ?></em>
+						<em class="query-notice-hint screen-reader-text"><?php _e( 'Search or use up and down arrow keys to select an item.' ); ?></em>
+					</div>
 					<ul></ul>
 					<div class="river-waiting">
 						<span class="spinner"></span>
@@ -1415,12 +1418,12 @@
 			</div>
 		</div>
 		<div class="submitbox">
+			<div id="wp-link-cancel">
+				<a class="submitdelete deletion" href="#"><?php _e( 'Cancel' ); ?></a>
+			</div>
 			<div id="wp-link-update">
 				<input type="submit" value="<?php esc_attr_e( 'Add Link' ); ?>" class="button button-primary" id="wp-link-submit" name="wp-link-submit">
 			</div>
-			<div id="wp-link-cancel">
-				<a class="submitdelete deletion" href="#"><?php _e( 'Cancel' ); ?></a>
-			</div>
 		</div>
 		</form>
 		</div>
Index: src/wp-includes/css/editor.css
===================================================================
--- src/wp-includes/css/editor.css	(revision 29256)
+++ src/wp-includes/css/editor.css	(working copy)
@@ -79,19 +79,21 @@
 }
 
 .mce-textbox,
-.mce-checkbox i.mce-i-checkbox {
+.mce-checkbox i.mce-i-checkbox,
+#wp-link .query-results {
 	border: 1px solid #ddd;
 	-webkit-border-radius: 0;
 	border-radius: 0;
 	-webkit-box-shadow: inset 0 1px 2px rgba(0,0,0,0.07);
 	box-shadow: inset 0 1px 2px rgba(0,0,0,0.07);
-	-webkit-transition: .05s border-color ease-in-out;
-	transition: .05s border-color ease-in-out;
+	-webkit-transition: .05s all ease-in-out;
+	transition: .05s all ease-in-out;
 }
 
 .mce-textbox:focus,
 .mce-textbox.mce-focus,
-.mce-checkbox:focus i.mce-i-checkbox {
+.mce-checkbox:focus i.mce-i-checkbox,
+#wp-link .query-results:focus {
 	border-color: #5b9dd9;
 	-webkit-box-shadow: 0 0 2px rgba(30,140,190,0.8);
 	box-shadow: 0 0 2px rgba(30,140,190,0.8);
@@ -1061,7 +1063,6 @@
 
 #wp-link-close {
 	color: #666;
-	cursor: pointer;
 	padding: 0;
 	position: absolute;
 	top: 0;
@@ -1069,6 +1070,9 @@
 	width: 36px;
 	height: 36px;
 	text-align: center;
+	background: none;
+	border: none;
+	cursor: pointer;
 }
 
 #wp-link-close:before {
@@ -1087,6 +1091,16 @@
 	color: #2ea2cc;
 }
 
+#wp-link-close:focus {
+	outline: none;
+	-webkit-box-shadow:
+		0 0 0 1px #5b9dd9,
+		0 0 2px 1px rgba(30, 140, 190, .8);
+	box-shadow:
+		0 0 0 1px #5b9dd9,
+		0 0 2px 1px rgba(30, 140, 190, .8);
+}
+
 #link-selector {
 	padding: 0 16px 50px;
 }
@@ -1135,6 +1149,11 @@
 	margin: 3px 0;
 }
 
+#wp-link p.howto a {
+	text-decoration: none;
+	color: inherit;
+}
+
 #wp-link-search-toggle {
 	cursor: pointer;
 }
@@ -1198,17 +1217,46 @@
 	top: 205px;
 }
 
-#wp-link li,
-#wp-link .query-notice {
+#wp-link li {
 	clear: both;
 	margin-bottom: 0;
 	border-bottom: 1px solid #f1f1f1;
 	color: #333;
-	padding: 4px 6px;
+	padding: 4px 6px 4px 10px;
 	cursor: pointer;
 	position: relative;
 }
 
+#wp-link .query-notice {
+	padding: 0;
+	border-bottom: 1px solid #dfdfdf;
+	background-color: #f7fcfe;
+	color: #000;
+}
+
+#wp-link .query-notice .query-notice-default,
+#wp-link .query-notice .query-notice-hint {
+	display: block;
+	padding: 6px;
+	border-left: 4px solid #2ea2cc;
+}
+
+#wp-link .unselectable.no-matches-found {
+	padding: 0;
+	border-bottom: 1px solid #dfdfdf;
+	background-color: #fef7f1;
+}
+
+#wp-link .no-matches-found .item-title {
+	display: block;
+	padding: 6px;
+	border-left: 4px solid #d54e21;
+}
+
+#wp-link .query-results em {
+	font-style: normal;
+}
+
 #wp-link li:hover {
 	background: #eaf2fa;
 	color: #151515;
@@ -1285,6 +1333,7 @@
 
 #wp-link-cancel {
 	line-height: 25px;
+	float: left;
 }
 
 #wp-link-update {
Index: src/wp-includes/js/wplink.js
===================================================================
--- src/wp-includes/js/wplink.js	(revision 29256)
+++ src/wp-includes/js/wplink.js	(working copy)
@@ -31,6 +31,11 @@
 			rivers.recent = new River( $( '#most-recent-results' ) );
 			rivers.elements = inputs.dialog.find( '.query-results' );
 
+			// Get search notice text
+			inputs.queryNotice = $( '#query-notice-message' );
+			inputs.queryNoticeTextDefault = inputs.queryNotice.find( '.query-notice-default' );
+			inputs.queryNoticeTextHint = inputs.queryNotice.find( '.query-notice-hint' );
+
 			// Bind event handlers
 			inputs.dialog.keydown( wpLink.keydown );
 			inputs.dialog.keyup( wpLink.keyup );
@@ -43,10 +48,19 @@
 				wpLink.close();
 			});
 
-			$( '#wp-link-search-toggle' ).click( wpLink.toggleInternalLinking );
+			$( '#wp-link-search-toggle' ).on( 'click', wpLink.toggleInternalLinking );
 
 			rivers.elements.on( 'river-select', wpLink.updateFields );
 
+			// Display 'hint' message when search field or 'query-results' box are focused
+			inputs.search.add( rivers.elements ).on( 'focus.wplink', function() {
+				inputs.queryNoticeTextDefault.hide();
+				inputs.queryNoticeTextHint.removeClass( 'screen-reader-text' ).show();
+			} ).on( 'blur.wplink', function() {
+				inputs.queryNoticeTextDefault.show();
+				inputs.queryNoticeTextHint.addClass( 'screen-reader-text' ).hide();
+			} );
+
 			inputs.search.keyup( function() {
 				var self = this;
 
@@ -335,6 +349,8 @@
 			} else if ( key.TAB === event.keyCode ) {
 				id = event.target.id;
 
+				// wp-link-submit must always be the last focusable element in the dialog.
+				// following focusable elements will be skipped on keyboard navigation.
 				if ( id === 'wp-link-submit' && ! event.shiftKey ) {
 					inputs.close.focus();
 					event.preventDefault();
@@ -387,12 +403,13 @@
 			};
 		},
 
-		toggleInternalLinking: function() {
+		toggleInternalLinking: function( event ) {
 			var visible = inputs.wrap.hasClass( 'search-panel-visible' );
 
 			inputs.wrap.toggleClass( 'search-panel-visible', ! visible );
 			setUserSetting( 'wplink', visible ? '0' : '1' );
 			inputs[ ! visible ? 'search' : 'url' ].focus();
+			event.preventDefault();
 		}
 	};
 
@@ -502,7 +519,7 @@
 
 			if ( ! results ) {
 				if ( firstPage ) {
-					list += '<li class="unselectable"><span class="item-title"><em>' +
+					list += '<li class="unselectable no-matches-found"><span class="item-title"><em>' +
 						wpLinkL10n.noMatchesFound + '</em></span></li>';
 				}
 			} else {