Neil's Place

October 30, 2003

Bug 7639 is fixed!
This is the fix so that now works on XML UI languages
The article wins this years 'Largest use of Acronyms' award (115 uses)

10:25 PM New Work

I've accepted a contract position with Mozdev Group to work on some Mozilla-related projects. Actually, I started on Monday so I've already done some work already. It's always good to work with folks who share the same vision as I do. Let's hope together we can build some exciting products and help to promote Mozilla technologies.

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October 29, 2003

5:28 PM Building Technologies with Baby Steps

When someone encounters somthing new, one has a tendency to compare it to something that already exists. This is a natural habit that everyone does to help provide a starting point for determining how to react to whatever this new thing is. For instance, when a new product is released, it will be compared to some existing product, and lists of advantages and disadvantages between the new and old will be created. It really doesn't matter that the new product has a very different purpose or not.

For instance, if you build a new revolutionary killer product that does all kinds of never-before-done things, but you put a Back button, and an address bar and Bookmarks on it, it is no longer a new revolutionary killer product, but just another web browser. It doesn't matter what you say, because people will look for the familiar in your new product, and compare your product to that. You can't create revolutionary products intentionally, so quit trying.

Why was XML successful? Likely much of its success was due its similarity to HTML. If XML had used square brackets or other different syntax, its possible that it wouldn't have gotten as far. People need a way to transition to new things so that familiarity is maintained thoughout the process. When building a new technology, you need to ensure that radical changes are minimal to encourage adoption.

For instance, a web developer that understands HTML forms would have no trouble with a few new tags or attributes added to HTML forms, but would really get lost when it comes to XForms. That would require one to grasp XML syntax, different tags for forms, the separation of UI and data, XPath, and a number of other things. The intuitive leap is just too great. Instead, technologies must be created which allow the developer to take baby steps from one concept to the other. In fact, Opera has provided an alternative to XForms which is much more transitional, and, if suitably implemented, would likely be more widely adopted.

I've mentioned XAML a number of times recently. It falls into the same category. People are looking for something familiar to compare XAML to, usually comparing it to XUL, since they are both XML languages for constructing user interfaces. They do have very different purposes though. XUL was primarily developed for constructing Mozilla's UI, and for constructing web oriented applications. It wasn't designed so one could write a better alternative to Microsoft Excel or Adobe PhotoShop. Thus, XUL builds on existing web technologies such as CSS and JavaScript. Web developers are familiar with these so the transition is much simpler and smoother. XAML, on the other hand, is a transition only for .NET developers since it contains things from there but contains almost nothing from the Web. The gap is much too large for web developers, which may mean that it may have trouble getting any usage by that group.

Have you noticed how popular the web is? The web has slowly changed the way that developers and companies think about things. You can't just light a match and blow it away. Progress is done in small steps.

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October 28, 2003

7:26 PM One more XAML thought

One thing I noted about XAML is that both the code and the XML parts need to be compiled before using them -- although the XAML can be interpreted by Explorer in some means, perhaps by compiling it when needed.

From what I can tell there is no XML at run-time, meaning no DOM-manipulation. You need to use all new APIs to manipulate the UI. Actually, the whole thing works very similar to Mac OS X, which stores UI descriptions in XML which map to classes. Apple doesn't promote this much though as they prefer that people use the visual tools.

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October 27, 2003

6:38 PM Some XAML comments

OK, I took a quick look at XAML to see how it compares to XUL, or anything.

  • It is indeed a XUL-like language for describing user interfaces. Why didn't they just use XUL? Well, you wouldn't expect MS to use something someone else created would you?
  • XAML might be only a codename. Sometimes, the documentation says it's a codename, and XAML always appears in quotes.
  • Only XAML files that don't have code can be displayed directly in IE. I'm not sure why you would have a non-code application. If your application contains code, it must be compiled into an executable. If I'm reading that right, it means that you can't do remote XAML. However, there is this Click-Once thing which appears to work exactly like Mozilla's XPInstall, by allowing one to install an application with one click. You still have to compile and set up all these deployment information, much like how XPInstall uses install.js scripts and RDF manifest files. There is a reference to 'application/xaml+xml' though, (Where's the x- or vnd.? Hello? Microsoft? Standards?) which I think is for non-code apps. It also means you need a compiler to develop with, conveneniently sold by Microsoft. XAML does not support interpreted languages like JavaScript (or JScript).
  • You can run compiled code in a standalone window or in a browser, but you can't do both. Switching requires recompiling.
  • Each 'XAML' tag corresponds to a Class. Attributes on the tags correspond to the fields (properties) of the class. For example, a Button class can be specified with <Button Width="100" FontSize="10">
  • There is no CSS used -- instead specific attributes are used. There is something confusingly called Styles, which appear to be more like CSS classes for sharing appearance with a number of elements. This Styles feature does seem to have the capability to adjust the appearance of inner content, for example the thumbs and slider part of a scrollbar can be adjusted with a block of XML. In fact, some of the examples suggest that the Style features might have some XBL-like content capability, although it looked more confusing.
  • There's a databinding feature, kind of like the one IE already has which can bind to XML, SQL and so forth. In XUL, this is done with templates and RDF. In XAML, the data to bind to are even called data sources.
  • There's something which falls into the category of 'Yet another XML vector language which isn't SVG.' It does look very similar though, but my cursory glance and limited knowledge of SVG suggest that it isn't the same. It is called Windows Vector Graphics though. Yes, this is exactly what the world needs. More similar but different vector graphics languages.
  • As far as I can tell, there's no XBL or overlays or anything similar. Custom components can be created in native code (C# or whatever). So, there's isn't anything as cool as Firebird Extensions.
  • The documentation is, like most of the stuff on MSDN, difficult to navigate through. Most of it is vague and more of a reference. There is only a few pages that actually explain how to do something. Because of this, there may be something I'm missing. There may be more interesting features that I missed, but I don't think XAML itself is necessarily all that powerful. In fact, it's really just a mapping between classes and XML.

There's a general overview here.

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5:21 PM XAML Info now available

XAML info is now available. I haven't looked at it yet, but it's rumoured to be similar to XUL. More comments to come soon.

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1:09 PM XUL-related quotes from Hixie

Ian Hickson has some interesting quotes from a recent XUL naming debate between him and, if you've been following XUL, you should know who else.

We stopped working on the XUL spec itself when XUL Planet started documenting XUL in more detail than we had time to do ourselves.


Most of the current XUL work is being done within standards organisations with strict NDA policies. If you are a ISO, W3C, ECMA, or IETF member let me know and I can show you the relevant links... I'm under NDA from one of the above groups, in which XUL is being discussed.

and even:

XUL _is_ in active development, we are currently taking feedback into account and are more carefully defining the XUL box model.

All quotes from here.

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October 26, 2003

XUL Boxes in Safari
Dave Hyatt informs us that Safari now has support for the xul-box layout type

October 25, 2003

7:14 PM Custom XUL Rendering Widgets

I've been thinking a bit over the last week or so about support for custom drawing widgets in Mozilla. There are four possibilities:

  • Create a <canvas> tag as described in bug 102285. Although the patch needs some work, this is probably the easiest approach. However, it limits one to a single special XUL tag for drawing.
  • Create a modifiable image object. The image would have a variety of drawing functions such as drawLine, drawRect and so forth as well as pixel-level functions. It might even be possible to support transparency and animation as existing images do. It could then be used in the HTML and XUL image tags, or even CSS properties if a method was created to assign custom images to them. The canvas tag patch suggests that this technique would be quite simple to implement. It has the advantage that it could work on various different tags.
  • Create an interface with drawing functions. These would be called by the application during paint events (such as onpaint) to update the display. This would have the advantage of not necessarily requiring a buffer to hold image data, but would be slower for repeated redraws. It would however, allow extra components to implement the drawing interface, allowing for various alternate system-specific libraries to handle drawing.
  • Use SVG. This is the most work, but only really handles some cases. SVG requires a DOM node for every part of what is to be drawn, which isn't practical for pixel-level drawing or heavy animation.

There's also some security issues, for example, to ensure that unprivileged code either can't use custom drawing, or can't draw over things it shouldn't be able to.

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October 24, 2003

11:20 PM XUL and XAML

A lot of people (here and here, for example) are discussing XAML, an upcoming MS technology which many think is similar to XUL. In case people are confused, no-one has actually seen XAML yet; we only have rumours as to what it is.

The only thing we know is that it is a markup language for describing applications and possibly a few clues from a screenshot. In fact, I don't think we even know for sure that it's for describing user interfaces at all. In fact, if it can, it may be a 'side effect' of what it's actual purpose is.

I suspect the goals of XAML are quite different from the goals of XUL (apart from any MS evil conspiracy). For instance, XUL is designed to be a cross-platform UI language, akin to HTML, that uses existing Web standards such as CSS, XML, DOM, RDF and so on, and includes some interesting features such as overlays and XBL for extensibilty. In my opinion, the only missing things could be fixed up in time with a few good developers who can dedicate themselves to it.

XAML might be similar (complete speculation, remember), but wouldn't think it used CSS or JavaScript. We find out next week sometime what XAML actually is, and then we can determine how similar or different it is.

One of the difficulties in promoting XUL and Mozilla is that many people have this misconception that XUL shouldn't be used because IE has more users. That's unfortunate. That confusion is created because people hear the name Mozilla, and immediately lump it in the 'browser' category, forever more being known only as an IE competitor, not as something more. There's really no reason to do this of course. A better way to think is to allow room for both Mozilla and IE. There really isn't any reason to think that just because a user uses IE for browsing that they shouldn't use a mail reader or an RSS reader or an IM client that doesn't use Mozilla technology such as XUL or the Gecko engine.

So, even if there are lots of competing XML UI languages (and there are many), there's no reason to think you need to use one or the other because one is more popular.

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