Search help by the TemplateEngine from yacy

I am looking for someone who can explain the basis of the template engine to me.

What I have found so far is the assignment of variables via the properties, i.e. individual variables and the loops.

What I don’t understand exactly are the if clauses as well as whether logical operators are present?

Where exactly is the specification or are there any reference works?

I found Documentation for the engine:

and the codebase on:

This means I don’t really need any more help, but I would still like to discuss the possibility of expanding the “engine”