Adobe Dreamweaver has dominated the Web-editing field for longer than most people can remember, but in the past few years it has seemed willing to coast on its reputation, offering worthy but uncompelling upgrades with each recent version. Dreamweaver CS6 version is different. It’s an essential upgrade for anyone who wants to build Web pages or apps that automatically adapt when viewed in a Web browser on a phone or tablet or a browser on a laptop or desktop. For the past few years, I’ve been doing most of my Web design in Microsoft’s clean, efficient, and underpublicized Expression Web, but Dreamweaver CS6 is the first Web editor built for the multiplatform era, with full support for HTML5 and CSS3. Like the rest of the CS6 suite, Dreamweaver is targeted to professionals who are willing to climb its steep learning curve, but even occasional coders can use it to build impressive-looking sites.

The big new features in Dreamweaver are these. First is “fluid grid layouts” that let you specify exactly how page elements will be arranged when your site is displayed on a small-screen phone, a midsize tablet, or a full-screen desktop. (Keep reading for more detail on this.) Next is built-in support for PhoneGap Build, an open-source platform that makes it easy to create a single Web-based app that runs on multiple phone platforms. Dreamweaver also improved its integration with Query Mobile, a JavaScript-based platform for building browser-based phone and tablet apps. CSS Transitions—the Web-based counterpart of transitions in traditional presentation apps—are now supported through a reasonably intuitive interface.

Adobe has improved the fidelity and flexibility of Dreamweaver’s “Live” preview, and improved its “multiscreen” preview panel that shows what your page will look like at phone, tablet, and desktop screen sizes. Adobe’s online “browser lab” makes it possible to test your pages on older browser platforms, though Microsoft’s comparable SuperPreview feature offers an even wider choice of old and new browsers to test in.

Another Dreamweaver feature that I’ve wanted for years, and which Adobe scarcely mentions in its PR, is built-in Web font support through a simple dialog that lets you install fonts to your Web server so you can use them on your pages; this was always possible through laborious hand-coding but Dreamweaver makes it easy. Other improvements that I’m glad to see include a completely revamped—and speedy—FTP module with full support for secure protocols. Built-in support for the W3C Consortium’s page-validation tool guarantees full compliance with current Web standards.

The most spectacular new feature in Dreamweaver is its support for “fluid grid layouts,” which means that it creates pages organized according to an invisible underlying grid that changes according to the size of the screen. Text and graphic elements on the page automatically readjust their position when the page is viewed on a phone, tablet, or desktop. I had to watch a demo video (accessible from Dreamweaver’s opening menu) to figure out to use it, but after that it was easy.

You create a fluid grid layout by targeting three screen sizes: phone, tablet, and desktop. First you arrange the page elements as you want them to look at one screen size, with each element aligned to the invisible background grid. Then you click an icon to switch to a different screen size, and arrange the elements in a different way on the grid. So, for example, a phone will display your whole page in a single column with a dropdown navigation menu at the top, while a tablet will display parts of the page in three columns, with a wide navigation bar at the top. The underlying CSS automatically switches between layouts according to the screen size of the device displaying the page. The multiscreen preview panel lets you change any or all of the three built-in screen sizes, so you can test the way the fluid grid will work on any size you want.

Dreamweaver, predictably, is tightly integrated with Adobe’s Flash format. But if you’re developing for iOS, you can’t use Flash in your apps or Web pages, unless you buy Adobe’s $4,500 Flash Media Server to stream Flash in a way that iOS permits. Dreamweaver let me drop Flash video into my Web pages without an hiccup and with plenty of layout options, but when I tried to add HTML5 video to my page, I had to figure out for myself that I needed to download and install an HTML5 Video “widget” and then modify the widget’s code by hand.

Like the rest of the Adobe’s Creative Suite Dreamweaver’s interface is a forest of panels and “tab groups” and toolbars that takes time to get used to. Unlike the rest of the suite, which uses a graphic interface to edit graphic objects like animations, photos, illustrations, and printed pages, Dreamweaver’s graphic interface is a set of tools for editing raw HTML, CSS, JavaScript, and other text-based code. Most of the time, you can use one of Dreamweaver’s GUI-based buttons and menus for modifying the underlying code, but sometimes you can’t and that means getting your hands dirty while editing the code directly. This is good if you know how to edit raw code, frustrating if you don’t. Sometimes, especially while working with the new fluid layout grid feature, I gave up trying to find a menu or toolbar for modifying a layout detail, and had to dig through the raw code to make the change. The fluid layout grid feature is obviously a work in progress, and future versions will make this kind of thing easier, but you should be prepared for some minor first-version frustrations in the meantime.

For basic HTML and CSS editing, I still tend to prefer Microsoft Expression Web 4, but Expression Web works only on Windows, while Adobe’s apps work more or less identically on Windows and Mac machines. Also, Dreamweaver CS6 is unquestionably the first and only Web-building tool that works smoothly and capably in the new multi-platform world. It’s got its rough edges, but Adobe Dreamweaver CS6 also has more power and flexibility than anything else in its category, and it deserves our Editor’s Choice.