I've been playing around with a theme for a ghost blog (ghost.org). It uses handlebars for its templates and I've been looking at existing ones to see what is possible and what isn't.
I have come across {{!< default}}. default is the name of a template.
What does !< mean?
If you look in the index.hbs file of the default theme you'll find this comment:
{{! The comment above "< default" means - insert everything in this file into
the {body} of the default.hbs template, which contains our header/footer. }}
It simply tells the page which parent template it should be inserted into