Is it possible to hook into the expression evaluation system?

[egges]

I'm using handlebars in a framework that generates text from templates and data. I was wondering if it is possible to provide a function that that does the actual expression evaluation. For example, I'd like my users to be able to do the following:

{{#if answer.toLowerCase().includes("hi")}}
You said hi!
{{else}}
Please try again...
{{/if}}

Or

Your answer is {{answer.toLowerCase()}}

I know that the system supports helpers, so I could use that mechanism. But it would be nice if there could be a default helper that is always called even if no helper is specified in the template.

Is something like this possible?