MozillaでXULファイルシステムがどのように構成されているかを見ることからはじめましょう。
Mozillaはコンポーネントを好きなだけインストールできるように構成されています。典型的なインストールはナビゲーター、メッセンジャーとエディタコンポーネントでしょう。またインストールされたこれら各々にスキンとロケールをもつこともできます。これらコンポーネントの各々、つまりパッケージは、そのためのユーザーインターフェイスを記述したファイルセットからなります。例えば、メッセンジャーコンポーネントにはメールメッセージリストウィンドウ、メッセージ作成ウィンドウ、アドレス帳ダイアログの記述があります。
Mozillaとともに提供されるパッケージはクロム(chrome)ディレクトリに置かれます。これはMozillaをインストールしたディレクトリにあります。クロムディレクトリはMozillaが使うユーザーインターフェイスを記述するファイル全てが置かれる場所です。
個々のパッケージには多くのサブパッケージがあるかもしれません。例えば、メッセンジャーパッケージには、二つのサブパッケージ、アドレス帳とメッセージ作成パッケージがあります。
パッケージはその一部としてそれ自身のスキン情報を提供することができます。あるいは標準のスキンに依存することもあります。
ユーザインターフェイスは、それぞれクロム(chrome)ディレクトリの中の別々のサブディレクトリに格納されている三種類のファイルで構成されます。これら三種類のファイルは内容(content)、スキン(skin)とロケール(locale)です。あるコンポーネントは一つ以上の標準のスキンやロケールを提供することがありますが、ユーザはそれを自分のもので置き換えることが出来ます。
Mozillaのchromeディレクトリを見てください。そこにはインストールされたパッケージ毎に一つずつ、多くのJARファイルがあるでしょう。例えば、messenger.jarというファイルはメッセンジャーコンポーネントのユーザインターフェイスを記述しています。modern.jarというファイルはモダン(Modern)スキンを記述しています。今のところ、あなたはまた、それぞれのJARファイルに対応したディレクトリがあるのを見ることでしょう。おそらく、これらのディレクトリはJARファイルへの変換が完了したらなくなることでしょう。このディレクトリは単に対応するJARファイルを解凍したバージョンです。
あなたはchromeディレクトリでrdfという拡張子を持ったいくつかのファイルも発見するでしょう。これらのファイルはインストールされたパッケージ、スキンやロケールのリストを記述しています。
The name of the JAR file might describe what it contains. However, you can determine for sure by viewing its contents. (You can view JAR files with a ZIP utility). Let's go through an example for a simple package, the messenger package.
If you extract the files in messenger.jar, you will find that it contains a directory structure like the following:
content
messenger
contents.rdf
messenger.xul
-- other mail XUL and JS files goes here --
addressbook
-- address book files go here --
messagecompose
-- message composition files go here --
.
.
.
This is easily recognizable as a content package, as the top-level directory is called 'content'. For skins, this directory will be called 'skin' and for locales, this directory will be called 'locale'. Actually, this isn't necessary but you should follow this convention to make your package clearer. Some packages may have more than one of a content, skin or locale. In this case, you will find a directory for each type.
The content/messenger directory contains a number of files with xul and js extensions. The XUL files are the ones with the xul extension. The files with js extensions are JavaScript files which contain scripts that handle the functionality of a window. Many XUL files have a script file associated with them.
In the listing above, two files have been shown. There are others of course, but for simplicity they aren't shown. The file messenger.xul is the XUL file that describes the main Messenger window which displays the mail messages list. The main window for a content package should have the package name with a xul extension. Some of the other XUL files are included by messenger.xul and others describe separate windows. For example, the file subscribe.xul is used for the dialog to subscribe to newsgroups.
The file contents.rdf is found in every package, one for each content, skin and locale in the package. This file will be described in detail later, but briefly, it is used to describe the contents of the package.
Two subdirectories exist, addressbook and messagecompose, which describe additional sections of the Messenger component. They are placed in different directories only to separate them.
The modern.jar and classic.jar files describe the skins provided with Mozilla. Their structure is similar to the content packages. For example, modern.jar:
skin
modern
navigator
contents.rdf
-- navigator skin files go here --
messenger
contents.rdf
-- messenger skin files go here --
editor
contents.rdf
-- editor skin files go here --
communicator
contents.rdf
-- communicator skin files go here --
global
contents.rdf
-- global skin files go here --
.
.
.
Here, five directories exist, one for each package that the skin is applied to. For example, the editor directory describes the skin for the editor component. The global directory contains skin files that all general to all packages. These files will apply to all components. You will usually use this one yourself.
You might notice that there are five contents.rdf files. This is so the skins are applied separately to each component. You could have a different skin for navigator as messenger, although most of the appearance is determined by the global part so you won't see much difference. They are also separate files so that new components can be added and existing components can be removed easily.
A skin is made up of CSS files and a number of images used to define the look of an interface. The images are used for the toolbar buttons. The file messenger.css is used by messenger.xul and contains styles with define the look of the mail toolbars, and the messages list.
By changing the CSS file, you can adjust the appearance of a window without changing its function. This is how you can create a skin.
The file en-US.jar describes the language information for each component, in this case for US English. Like the skins, each language will contain files that specify text used by the package but for that language.
As usual, a contents.rdf file is provided that lists the packages the locale provides text for. Sundirectories provide the text for each package.
The localized text is stored in two types of files, DTD files, and properties files. The DTD files have a dtd extension and contain entity declarations, one for each text string that is used in a window. For example, the file messenger.dtd contains entity declarations for each menu command. In addition, keyboard shortcuts for each command are also defined, because they may be different for each language. DTD files are used by XUL files, so in general, you will have one per XUL file.
Properties files are similar, but are used by script files. The file messenger.properties contains a few such strings.
This structure means that to turn Mozilla or a component into a different language, one only needs to add a new locale for that language.
Many of the packages in Mozilla are sub-packages of the communicator package. For example, you'll find the bookmarks window, the history viewer and the preferences dialogs within the communicator package. They are put there because they are general to a number of packages. There is nothing special about them.
One special package is the one called toolkit. (or global). We saw the global directory earlier for skins. The toolkit.jar contains the corresponding content for it. It contains some global dialogs and definitions. It also defines the default appearance and functionality of the various widgets such as textboxes and buttons. The file global.css located in the global part of the skins directory contains the default look for all of the XUL interface elements. Most skin changes will involve variations of this file.
The structure described above is where the default packages, skins and locales are stored. However, they do not have to be placed there. If you have another package installed, it may be placed anywhere. The RDF files in the chrome directory store the list of installed packages, skins and locales and where they are located.
A user may have multiple skins and locales installed that both modify the same package. Only one skin and locale per package is active at any given time. The RDF files also specify which skins and locales are active.
(Next) In the next section, we'll look at how to refer to files in the chrome structure.