This is the inner platform effect. As an application grows, its configuration expands until it became a programming language, except bug-ridden, underspecified

This is the inner platform effect. As an application grows, its configuration expands until it became a programming language, except bug-ridden, underspecified and with terrible ergonomics. The configuration-bankruptcy is declarer and a new configuration format is picked. Rinse, repeat. The format itself is not without blame of course: the more flexible it is, the more easily can be repurposed into a (bad) programming language. Having committed this mistake over and over, these days, I would pick the simplest config format possible (even .ini might be too powerful) for basic configuration, and delegate more complex "configuration" to a real programming language (possibly the same language the application is written in).