<!-- Lisp Editor -->
<extension point="org.eclipse.ui.editors">
<editor
name="Lisp Editor"
extensions="lisp,cl,el"
icon="icons/lispFile.gif"
contributorClass="org.eclipse.ui.texteditor.BasicTextEditorActionContributor"
class="jasko.tim.lisp.editors.LispEditor"
id="jasko.tim.lisp.editors.LispEditor">
</editor>
</extension>
Add your preferred extension to the "extensions" attribute, and start
up Eclipse. That should do the trick.