It's a horribly restrictive syntax. Instead of allowing modularity and flexibility in how I structure parts of the config, I'm instead locked into this indentation-obsessed and sparse file that forces me to learn the exact mental model of whoever designed the yaml.

Almost nobody uses explicit typing in yaml.

The fact you need features like folding strings or chomp characters is a symptom that yaml is trying to work around limitations that shouldn't be there to begin with.