Freemarker - Defining custom build-ins / filters

Question

Is it possible to define a custom build-ins (name no longer will be suitable) in ftl?
I don't want to make it a function but instead a build-in, because of semantic premises.

Answer 1

It's not possible, the ? syntax is reserved for the built-in functions. (This meant to change in the future BTW. Sadly, in the far future, judging from the size of the backlog before it and the pace it's eliminated...)