Bug 123040 [Commands] request: display help topic
I'm going to attach a patch to "command-ify" the opening of help topics. The command takes a parameter which is the href of a help topic. The default handler uses IWorkbenchHelpSystem.displayHelpResource(String) with the href parameter. If no parameter was given, the default handler calls IWorkbenchHelpSystem.displayHelp() instead to simply open the help system. Note that this looks like it should be opened against User Assistance, but the plugins that should be patched (I think) are org.eclipse.ui and org.eclipse.ui.workbench, so I opened against UI.
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/ParameterizedCommand.java
* Executes this command with its parameters. This does extra checking to
	 * see if the command is enabled and defined. If it is not both enabled and
	 * defined, then the execution listeners will be notified and an exception
	 * thrown.
	 * 
	 * @param trigger
	 *            The object that triggered the execution; may be
	 *            <code>null</code>.
	 * @param applicationContext
	 *            The state of the application at the time the execution was
	 *            triggered; may be <code>null</code>.
	 * @return The result of the execution; may be <code>null</code>.
	 * @throws ExecutionException
	 *             If the handler has problems executing this command.
	 * @throws NotDefinedException
	 *             If the command you are trying to execute is not defined.
	 * @throws NotEnabledException
	 *             If the command you are trying to execute is not enabled.
	 * @throws NotHandledException
	 *             If there is no handler.
	 * @since 3.2
	 */
	public final Object executeWithChecks(final Object trigger,
			final Object applicationContext) throws ExecutionException,
			NotDefinedException, NotEnabledException, NotHandledException {
		return command.executeWithChecks(new ExecutionEvent(command,
				getParameterMap(), trigger, applicationContext));
	}
	/**
	 * Returns the base command. It is possible for more than one parameterized