I would like to present HUML, a new (and experimental), simple, strict, serialization language for documents, datasets, and configuration. It prioritizes strict form for human-readability. It looks like YAML, but tries to avoid its complexity, ambiguity, and pitfalls.
HUML was primarily born out of the numerous frustrations with YAML, where one easy-to-miss, accidental indentation change can dangerously alter the semantics of a document. Other popular markup languages such as TOML and HCL are configuration-oriented. NestedText is an interesting approach, but is too primitive to be suitable for wider use cases. JSON is universal, but lacks comments, does not have a strict form for consistent readability across contexts, and has bracket-matching and formatting woes which make human editing difficult. Of these, YAML is the one that comes closest to indicating structure and hierarchy visually, but unfortunately, YAML is a dangerous, human-unfriendly minefile.
Ultimately, a new markup language is a subjective endeavour (it was even in 2001, as evidenced by YAML's original name, Yet Another ...). HUML looks like YAML, but borrows characteristics from many existing languages with the primary focus on enforcing human readability and consistency across contexts.
Still, why YET another markup language? ... Why not!?