Mallard Conditional Processing

We’ve talked about doing run-time conditional processing in our help for a very long time, nearly as long as I’ve been around. When you have applications that can run in multiple environments, you sometimes need to write different help text for difference cases.

For example, take an instant messaging application like Empathy. In GNOME 3, the Telepathy integration means that users can chat directly from the tray. Hackers know it’s not actually Empathy, but users don’t care. It’s chat. In GNOME 2, you usually interact with Empathy through the notification tray. In Unity, it integrates with the messaging menu. These are all things we should write about in the help.

But it’s hard to write about things when you don’t know where your help is read. The only way to deal with this is to patch the help for different environments. My experience is that that rarely happens. Plus, you don’t always create different packages for different environments. The exact same Empathy package in Fedora is used in GNOME Shell, GNOME fallback, and XFCE.

Other XML formats have conditional processing, but their design isn’t suitable for our needs. They usually work by having a set of attributes that take some tags. The behavior isn’t usually specified, because it’s assumed that they’ll be handled by a vendor-specific build tool that strips things out before creating a deliverable. Our source format is our deliverable format, and we want to adapt it at run-time.

So I’ve just landed some changes in Yelp to support a Mallard extension format for run-time conditional processing. Any block element can have the if:test conditional attribute added. This is evaluated as an XPath expression with extension functions that can tell you things about the environment. This is much more flexible than a set of tagging attributes, because you can combine multiple tests with “and” and “or“.

<p if:test="if:env('gnome-shell')">This is only shown in GNOME Shell</p>
<p if:test="if:env('gnome-shell') or if:env('gnome-panel')">
  This is shown under GNOME Shell or GNOME Panel

The if:test attribute is a convenient short-hand syntax. There are also conditional processing elements that allow you to do basic branching and fallback.

  <if:if test="if:env('unity')">
    <p>You're using Unity</p>
  <if:if test="if:env('xfce')">
    <p>You're using XFCE</p>
    <p>You're using something else</p>

The full syntax has another advantage. What happens if you hand a document with conditional processing to a Mallard processor that doesn’t support it? It turns out that Mallard has very well-defined rules for how unknown extensions are handled. In the first case, you just have an external attribute on a known element. The attribute is ignored and the p element is processed as normal.

In the second case, you have an external element in a block context. A Mallard implementation that doesn’t do conditional processing will visit the children in restricted block context. In restricted block context, unknown external elements are ignored.

Yelp 3.0 doesn’t have the conditional processing support. The following two snippets will do what they say in Yelp 3.0, but they will be exactly equivalent to Yelp 3.2 with conditional processing support.

<p if:test="if:env('foo')">
  This will be displayed in Yelp 3.0
  <if:if test="if:env('foo')">
    <p>This will not be displayed in Yelp 3.0</p>

Details are all subject to change, of course. This does basically follow a proposal I made to the Mallard mailing list last August. But for now, it’s in an experimental namespace. I just need to iron out the kinks and write up a specification on

Open Help Conference

Passive Voice Day

It has been decided that tomorrow, April 27, is Passive Voice Day. (It might be asked, “It has been decided by whom?” Exactly.) Passive voice should be written and spoken in by everybody. For one day only, active voice will be frowned upon. It might be considered silly by you, but it will be found to be fun by many.

The #passivevoiceday hashtag should not be forgotten when tweets are written, although it is doubted that passive voice sentences will be able to be fit into 140 characters.

ITS Tool Released

Last October, I blogged about itstool, a tool I developed to translate XML documents with PO files using ITS rules. Today, I released version 1.0.0 of ITS Tool on the new ITS Tool web site. If you’ve used xml2po before, you’re familiar with the basic idea: PO messages are extracted from an XML files, and translated messages are merged with the source to produce localized XML files. If you’re not already translating your documents using a message-based format, you need to start. Your translators will thank you.

ITS Tool takes the same idea as tools like xml2po, but the implementation is done entirely in terms of rules from the W3C Internationalization Tag Set. You don’t have to patch it to create a mode for a new XML format. You just need to provide a standard ITS file. Better still, if you mix XML vocabularies in a single file, ITS Tool can apply the rules for all matching formats.

Translators will be happy to know that we can now mark things as untranslatable using the standard its:translate attribute, or using custom its:translateRule elements. This is a long-requested feature that will help cut down the amount of unnecessary cruft that translators have to look at.

In addition to the features we get from standard ITS data categories, ITS Tool provides some custom extension rules to support features like translator credits and external file tracking. There are a few more features I’d like to provide as well, such as adding extra Mallard link titles and specifying transliteration-only messages.

I’ll be working on the GNOME build tools to switch GNOME’s documentation over to itstool for 3.2. Most messages in the PO files will be the same as with xml2po, so it won’t introduce much extra work for translators.

But ITS Tool is not just a GNOME project. It’s free software, under the GPL 3. It’s built on Python and libxml2, and can be used by any project for their XML documents. If you use an XML format that isn’t handled by the built-in ITS rules, you can pass your own custom ITS rules. Or if it’s a common format, submit those rules upstream. I encourage everybody working with XML documents to try ITS Tool and let me know how well it works and what can be done to improve it.

Open Help Conference


I’ve never been more excited to be a GNOME developer. After years of hard work and planning, GNOME 3 was released yesterday. Check out the Introduction to GNOME from our brand-new help to learn all about it.

GNOME 3 shows the innovation that open source communities can bring. Hundreds of developers, designers, writers, testers, and translators worked hard to deliver an amazing new user experience. Among them are the fantastic people who helped create an all-new help system that rivals anything I’ve seen elsewhere. My release notes list Phil Bull, Jim Campbell, Tiffany Antapolski, Natalia Ruz Leiva, Shaun McCance, Paul Frields, Mike Hill, Aline Bessa, Marina Zhurakhinskaya, and Kelly Sinnott. If I missed anyone, I’m really sorry. It’s hard to keep track of so much awesome.

We tossed out the old manual (who reads those?) and started fresh with topic-oriented help, building on the dynamic Mallard language. The results are amazing. The initial release has 214 pages, carefully organized and cross-linked to help you find the information you need quickly and get back to your life. What is a workspace? Select files by pattern. Enter special characters.

Frederic Peters did amazing work on so all the new help is available online. But remember that all of this is available from the Help application on your GNOME 3 desktop. The help viewer was completely rewritten for GNOME 3, and I think you’ll really like what we’ve done.

By the way, if you want to meet up and learn about GNOME’s fresh approach to help, you should come to the Open Help Conference this June. At least Phil, Jim, and I will be there, and we’ll be joined by documentation teams from other great open source projects.

We’re not done yet.

Help needs to constantly improve and evolve as we learn more about what our users need. The GNOME documentation team is already hard at work on more pages and revisions to existing pages. We’ll be pushing updates to the help weekly. If you want to get involved, subscribe to our mailing list and send an email to

We also welcome drive-by contributions. One of the really nice things about topic-oriented documents with Mallard is that it’s easy to just write up a page about something without worrying about making revisions to an entire book. If you love using GNOME, a great way to contribute is by writing a short page about an awesome time-saving trick. We’ll put these under Tips & Tricks, and users worldwide will learn something cool because of you.