Support sub-expressions

[alifeee]

sub-expressions are very useful. They are supported by handlebars -> https://handlebarsjs.com/guide/expressions.html#subexpressions

For example, to use a "equality helper" in an "if helper"

{{#if (eq var1 var2)}}
  they are equal!
{{else}}
  they are not equal!
{{/if}}

I can try to help, but I am not really sure which piece of code to start with, as this is quite a generic request. It does not seem as if there is one part that "renders" the contents of the inside of a bracket, and one would have to do it oneself, per helper.