Fix #10567. Make sure quickIs matches correct class name.

src/event.js

@@ -16,7 +16,7 @@ var rnamespaces = /\.(.*)$/,
 			//   0  1    2   3      4         5
 			// [ _, tag, id, class, attrName, attrValue ]
 			quick[1] = ( quick[1] || "" ).toLowerCase();
-			quick[3] = quick[3] && new RegExp( "\\b" + quick[3] + "\\b" );
+			quick[3] = quick[3] && new RegExp( "(?:^|\\w)" + quick[3] + "(?:\\w|$)" );
 		}
 		return quick;
 	},

test/unit/event.js

@@ -2452,6 +2452,14 @@ test("delegated events quickIs", function() {
 	markup.find( "b" ).attr( "devo", "NO" );
 	check( "b", "b|[devo='NO'] p|.D" );
 
+	markup
+		.on( "blink", ".tricky", function() {
+			ok( false, "triggered on wrong class name match" );
+		})
+		.find( "p" )
+			.attr( "class", "tricky-match" )
+			.trigger( "blink" );
+
 	markup.remove();
 });