Developers in object-oriented languages, such as Java (for example, in Swing) and C# / VB.NET (for example, in Windows Forms, ASP.NET, WPF, and Silverlight) are keen to apply inheritance and re-use the components of their app user interfaces (in short UI). Controls are adapted to specific needs by extending basic UI classes, and controls are assembled into reusable parts of screens (commonly user or custom controls). Web developers want to be able to do the same: for example, extend a <button> tag, or encapsulate a piece of markup for re-use, or have a simple way to bind data to an HTML element. But until now this wasn't possible in web development. This is exactly the promise of web components: extending HTML, they bring to web development what OO-developers expect in their toolkit. Web components enable you to specialize HTML elements with style and code, and W3C is actively engaged in the standardization of this technology. They can be thought...