and add "Foo" to the services.sync.registerEngines preference (it's a comma separated list of engine names).
== Updating the Weave preferences screen ==
Add a preference to turn your sync engine on/off by adding a line to <tt>weave/defaults/preferences/sync.js</tt> like so:
pref("extensions.weave.engine.foo", true);
Default to true or false as you see fit.
Add a check box to the preferences screen to enable the user to change this setting, by adding a line to <tt>weave/chrome/content/fx-preferences.xul</tt> like this:
<preference id="extensions.weave.engine.passwords"
name="extensions.weave.engine.passwords"
type="bool"/>
right after all the other similar preferences.
Finally, the preferences screen for Fennec is constructed separately, so to add your check box to the Fennec prefs screen as well you'll need to edit one more file. Open up <tt>weave/chrome/content/fennec-preferences.xul</tt> and add:
<pre>
<richpref pref="extensions.weave.engine.foo"
title="Foo" type="bool">
Sync foo
</richpref>
</pre>
right after the similar preferences.
[TODO: Explain better where to add these.]
== Testing and Debugging your Engine ==
TODO
