How to use comments in Handlebar templates?

Just add an exclamation mark after the opening brackets.

Normal Expression:

{{expressions}}

Commented Expression:

{{!expressions}}

The newest version of Handlebars has block comments support :

{{!-- {{commented expressions}} --}}

https://github.com/wycats/handlebars.js/commit/a927a9b0adc39660f0794b9b210c9db2f7ddecd9