Unable to get form validation to occur

[org.jenkins-ci]

Hello.

Please bear with me, as I've only been working with Jenkins for a
couple of days and am not yet familiar with the code and/or associated
libraries.

I'm trying to write a plugin to allow the use of the Fossil SCM
(http://fossil-scm.org).

I've defined a few configuration values for a given job (in
src/main/resources/hudson/plugins/albert/FossilSCM/config.jelly):

<?xml version="1.0" encoding="UTF-8"?>
<j:jelly xmlns:j="jelly:core" xmlns:f="/lib/form">
  <f:entry title="Repository URL" field="remote_url">
    <f:textbox/>
  </f:entry>
  <f:entry title="Branch" field="branch">
    <f:textbox default="trunk"/>
  </f:entry>
  <f:entry title="Repository database" field="repository_file">
    <f:textbox/>
  </f:entry>
</j:jelly>

And have created the required FossilSCM class:

public final class FossilSCM extends SCM
{
  private final String        remote_url;
  private final String        branch;
  private final String        repository_file;
  private static final Logger logger;

  static {
    logger = Logger.getLogger(FossilSCM.class.getName());
  }

  @DataBoundConstructor public FossilSCM(
    final String remote_url,
    final String branch,
    final String repository_file)
  {
    this.remote_url = remote_url;
    this.branch = branch;
    this.repository_file = repository_file;

    FossilSCM.logger.log(Level.WARNING, "FossilSCM: " + this);
  }

  public String getBranch()
  {
    return this.branch;
  }

  public String getRemoteUrl()
  {
    return this.remote_url;
  }

  public String getRepositoryFile()
  {
    return this.repository_file;
  }

  /* ... */
}

And the (apparently) required DescriptorImpl as a static inner
class:

  @Extension public static final class DescriptorImpl extends
    SCMDescriptor<FossilSCM>
  {
    private static final Logger log;

    static {
      log = Logger.getLogger(DescriptorImpl.class.getName());
    }
    public DescriptorImpl()
    {
      super(FossilSCM.class, null);
      this.load();
    }

    /**
     * Called by the Jelly config form to validate the Fossil
     * repository URL field.
     * 
     * Note that the name of this method is significant.
     */

    @SuppressWarnings({ "static-method", "unused" }) public
      FormValidation
      doCheckRemoteUrl(
        @QueryParameter final String value)
    {
      DescriptorImpl.log.log(Level.WARNING, "doCheckRemoteUrl " +
    value);

      try {
        new URI(value);
      } catch (final URISyntaxException e) {
        return FormValidation.error("This is not a valid URI");
      }

      return FormValidation.ok();
    }

    @Override public String getDisplayName()
    {
      return "Fossil SCM";
    }
  }

Going by:

https://wiki.jenkins-ci.org/display/JENKINS/Basic+guide+to+Jelly+usage+in+Jenkins#BasicguidetoJellyusageinJenkins-Formvalidation

This should apparently be enough to validate the "remote_url" field.
However, upon entering a value into the field and saving the job...
Nothing happens. The doCheckRemoteUrl() method is never called and any
value is accepted.

What am I doing wrong?

Is there better documentation available? I seem to be working entirely
from out-of-date and/or incorrect examples.

Regards,
M