ZimletTemplateFiles
Zimlet template files (actually Zimbra template files) are Javascript templates that work in a similar fashion to JSP - they are compiled from a html-fragment into a .js files using a tool found in Zimbra.
for example,
export CLASSPATH=/opt/zimbra/jetty/webapps/zimbraAdmin/WEB-INF/classes ~/bin/zmjava com/zimbra/kabuki/tools/templates/Template -p com_zimbra_hello_world.templates MainView.template
will generate the MainView.template.js file that is then sent to the browser if needed by the Zimlet.
declare template.js in the config.xml
<include>templates/MainView.template.js</include>
using template files from javascript
this.getHtmlElement().innerHTML = AjxTemplate.expand("com_zimbra_hello_world.templates.MainView#HelloWorldView_Main", params);
Future development suggestions
it seem to me that .template -> .template.js generation is currently rather haphazard. The .template.js is included in the zimlet config.xml in the same way as a hand written .js - Zimbra is not aware that this is actually a compiled artifact. It would (to my mind) be better for the config.xml to list package source, which it can then deal with as appropriate.