This is to say that they all leverage master pages - the technology in ASP.NET 2.0 that allows Web developers to factor content that is common to multiple pages in their sites onto a single (sometimes more) page. This page - the so-called master page - then becomes the central storehouse for shared content, which can be referenced and used by any other page in the application without duplication of code and/or content.

The question that I'm most often asked about master pages is: Why use master pages when I could achieve the same effect using frames or user controls? To these folks, I say: Once you've started master paging, you won't ever want to stop!

The problems - of which there are many - with HTML frames have to do with the fact that they do not result in the creation of a single, server-side ASP.NET page. Instead, they wind up dragging down multiple pages worth of HTML content for rendering into separate frames on the browser client. This means that each frame in a frames-based Web application becomes a separate entity with its own life cycle and path for communicating back with the server. This makes sharing information between pages that are running in different frames difficult, to say the least.

User controls seem like a great solution until the first time you actually build a substantial ASP.NET site using them. One of my first projects for Magenic required that I estimate an extension to an existing ASP.NET solution, which made extensive use of user controls. After looking at over 100 pages that consisted mainly of gray "user control" boxes with only a little dynamic content, it became clear to me that the poor design-time experience offered by user controls made them a bad choice for any situation that requires significant ASP.NET code reuse.

Master pages offer a mechanism for sharing ASP.NET elements across multiple pages with rich design-time support that allows you to see (though not change) your shared content on every page you load into Visual Studio 2005, albeit in half-color.

Thom Robbins's article on master pages, then, is a key article in our ASP.NET 2.0 focus for this issue. Also, be sure to check out Vishwas Lele's piece on AJAX-style development - the best coverage currently in print of what you can do with asynchronous callbacks in ASP.NET 2.0 today, prior to the launch of Microsoft's official Atlas offering for this purpose later this year.