3. RELAX NG example
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## 3. RELAX NG example

The RELAX NG example is similar to the other examples.

1. Create a subdirectory named `example3` in the `addon/` subdirectory of XXE user preferences directory:

2. Copy `example3.rnc`[4]to directory `addon/example3/`.

       default namespace = "http://www.xmlmind.com/xmleditor/schema/example3"
       namespace a = "http://relaxng.org/ns/compatibility/annotations/1.0"

       start = doc-element

       doc-element = element doc {
           para-element+
       }
       para-element = element para {
           mixed {
               [ a:defaultValue = "left" ]
               attribute align { "left" | "center" | "right" }?
           }
       }

3. Copy `example3.css` to directory `addon/example3/`.

       @namespace url(http://www.xmlmind.com/xmleditor/schema/example3);

       doc,
       para {
           display: block;
       }
       para {
           margin: 1ex 0;
       }
       para[align] {
           text-align: concatenate(attr(align));
       }

   This style sheet would work fine without default namespace declaration at the top of it but rule matching is faster when `@namespace` is used.

4. Create a document template for RELAX NG schema "`http://www.xmlmind.com/xmleditor/schema/example3`" using a text editor. Save it as `addon/example3/example3.xml`.

       <?xml version="1.0" encoding="UTF-8" ?>
       <doc xmlns="http://www.xmlmind.com/xmleditor/schema/example3">
         <para></para>
       </doc>

   Note that, unlike with DTDs and with W3C XML Schemas, there is no standard way to associate a RELAX NG schema to an instance[5].

5. Create a configuration file for XXE. Save it as `addon/example3/example3.xxe`.

       <?xml version="1.0" encoding="ISO-8859-1"?>
       <configuration name="Example3"
         xmlns="http://www.xmlmind.com/xmleditor/schema/configuration"
         xmlns:cfg="http://www.xmlmind.com/xmleditor/schema/configuration">
         <detect>
           <rootElementNamespace
             >http://www.xmlmind.com/xmleditor/schema/example3</rootElementNamespace>
         </detect>

         <relaxng compactSyntax="true" encoding="ISO-8859-1" location="example3.rnc"/>

         <css location="example3.css" name="Style sheet"/>

         <template location="example3.xml" name="Template"/>
       </configuration>

   The `relaxng` configuration element is essential because there is no standard way to associate a RELAX NG schema to an instance.

6. Restart XXE.

   Now you can use File → New and select Example3/Template to create a new document.

   ### Important

   Do not forget to temporarily disable the Schema cache (using Options → Preferences, Schema tab, Enable cache toggle) if you intend to develop your own schema and test it using XXE.

7. Make sure that the template document is valid: the red icon must not be displayed at the bottom/left of XXE window.

   If the template document, `example3.xml`, is invalid, please use a text editor and fix it because XXE is not designed to be comfortable to use with invalid documents.

[4] `Example3.rng` is also available in ``XXE_install_dir`/doc/configure/samples/example3/`, in case you prefer the XML syntax to the compact syntax.

[5] There is a non standard, proprietary, way to do that: the <?xxe-relaxng-schema location="..."?> processing instruction. However, its use should be restricted to testing and other quick and dirty experiments.

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