LZX source files are a particular type of text file: they are XML files. An XML-aware editor such as Eclipse, BBEdit, or Emacs (with psgml-mode or nxml-mode) will provide additional editing facilities such as automatic indentation, syntax highlighting (coloring markup characters such as < and tag names such as <canvas> ), and well-formedness checking (letting you know when you have an unbalanced < or quotation mark).

To configure an XML-aware editor to edit LZX files, you must configure it to edit those files in XML mode. This is done by registering the lzx extension with the XML mode of the editor. How to do this depends on the exact editor; this chapter gives instructions for some popular editors.

There are three types of schemas in popular use: DTDs, XSD, and RNG (and its associated format RNC). The LZX schema is distributed in each of these formats. They can be found in the lps/tools directory.

A Document Type Definition (DTD) is the oldest type, and is recognized by the most editors. Unfortunately, the DTD format is very weak compared with the other schema description languages, and can't indicate certain contextual information such as that a <dataset> can contain arbitrary XML. A DTD should only be used in an editor that doesn't support the other formats.

W3 and OASIS are standards bodies. The W3 standard for describing XML documents is the XML Schema Definition (XSD). The OASIS standard is RELAXNG. RNG and RNC files are RELAXNG files that contain schema definitions. RNG files are in XML; RNC files are intended to be human-readable.

There are four steps to using Eclipse with XMLBuddy

The lzx.el file tells emacs to recognize *.lzx files as XML files. With the DTD, this provides syntax-directed editing and validation of XML entities in LZX files.

If mmm-mode is installed, this file will also create an mmm submode to recognize the content of <method> and <script> tags as JavaScript, and direct mmm to use this submode for *.lzx files. This provides syntax coloring and intelligent indentation and navigation for JavaScript code within LZX files.

    (add-to-list 'load-path "path/to/mmm-mode-0.4.7")
    (load-library "mmm-mode")
    (require 'mmm-mode)
    (require 'lzx)

    (mmm-add-find-file-hook)

Also, the mark "[" is set to the point where you last entered insert mode. One often has the problem of wanting to leave insert mode where editing began. you can now do this with the following remapping

    imap ^D <ESC>`[

Now, if you hit control-D in insert mode, you leave where tou entered the insert mode.

Even more useful is the ability to repeat a previous command without changing the cursor position. Since this is pretty much always the behavior you want, you can remap ".", or you could use some other combination.

    noremap . .`[

OpenLaszlo applications can be written with a namespace:

  <canvas xlmns="http://www.laszlosystems.com/2003/05/lzx">...</canvas>

or without:

  <canvas>...</canvas>

If there is no namespace, the compiler defaults it to the LZX namespace (http://www.laszlosystems.com/2003/05/lzx").

As of OpenLaszlo release 3.1, the schema in lax.rnc has three deficiencies:

The difficulty is that the <class> tag in LZX actually extends the schema by adding new tags and attributes. We have a hand-written basic schema (WEB-INF/lps/schema/lzx.rnc) which is used to start with, but then user and system component libraries can extend the schema, depending on the application.

<window> , for example, is defined in a source library in lps/components/lz/window.lzx, so it is not in the base schema. So it is difficult to use a static RNG schema, because it needs to be modified as the app defines new classes.

The LZX compiler can be asked to give you the RNG schema from a source file, so something might be able to be hooked up to keep regenerating the schema from the source file, although it would be hard because the sources are often in an inconsistent state as you develop your application, so the parser has to be very forgiving about badly formed XML.

We have worked around the first problem with a transform of that schema that strips out the namespace declaration. That's tools/lzx+libraries-nons.rnc. We have worked around the second problem with a script that makes a copy of the schema and adds the components. This is tools/lzx+libraries.rnc. The third problem can't be fixed without modifying nxml-mode to either add declarations for <class> declarations that it sees, or request the schema for an application from the compiler. (From the command line, the --schema option does this.) OpenLaszlo does neither of these.

The LZX tag set is defined in a relax.ng schema located in the lps/tools directory.

If you are going to use the schema,

nxml-mode can be set to choose between these schemes automatically by pointing it at the schema locator file in tools/nxml-schemas.xml:

  (setq rng-schema-locating-files
      (append
       (list (substitute-env-vars "$LPS_HOME/tools/nxml-schemas.xml"))
       rng-schema-locating-files))

	Note
	(SUBSTITUTE-ENV-VARS isn't a standard gnu emacs functions; it's just a hack that we use in the .init file that has a few environment variables hardwired.)