A markup system plugin allows the use of markup syntax different from the standard FitNesse wiki markup.

The plugin registers itself with a name and a factory function:
public class PluginFeatureFactory extends PluginFeatureFactoryBase {

  public void registerMarkupSystems(MarkUpSystems systems) {
    systems.register(MyMarkup.NAME, MyMarkup::new);
    System.out.println(MyMarkup.NAME + " system registered");
    ... any initialization required ...

The markup system class must implement the MarkUpSystem interface:
public class MyMarkup implements MarkUpSystem {
  public static final String NAME = "mymarkup";
  ... implemented methods...

To use the new markup syntax, include a comment with the markup system name on the first line of the page:
#lang mymarkup
... page content ...

Other pages in the wiki will continue to use the standard wiki syntax.