OK, enough said. How does it work? Simple: Just use the <embed> tag. Here is a stripped down example:

<dialog>
	<tabbook>
		<tab [...]>
			[...]
		</tab>
		<tab label="Plot Options" i18n_context="Options concerning the plot">
			<embed id="plotoptions" component="rkward::plot_options"/>
		</tab>
		<tab [...]>
			[...]
		</tab>
	</tabbook>
</dialog>
	

What happens here, is that the entire GUI or the plot options plugin (except of course for the standard elements like Submit button, etc.) is embedded right into your plugin (try it!).

As you can see the syntax of the <embed>-tag is fairly simple. It takes an id as most elements. The parameter component specifies which plugin to embed, as defined in the .pluginmap file ("rkward::plot_options" is the result of concatenating the namespace “rkward”, a separator “::”, and the name of the component “plot_options”).