> An XML document with a well-thought-out domain-specific DTD would solve all these problems;

But then a YAML document written by disciplined and well-thinking people will also not have these problems.

Any of the complex formats work well when used in the most fitting way and go horribly wrong when people try to benefit too much from the complexity. XML was also a nightmare when put in the wrong hand, just as yaml is, and the next hyped and turing complete document syntax will be.