Currently, the schema consists of a mix of ad-hoc definitions and syntax.
This makes it hard to implement a tool to generically validate a given BIDS dataset.

In the ancpbids project (see below for link) we experimented with various schema definition languages, such as:

• XSD (XML Schema Definition): industry standard with mature support in many programming languages
• YAMALE: a community effort to formalize data structures using YAML format

Since the BIDS community is more comfortable with JSON/YAML formats, I would like to propose using a more formal schema definition language such as YAMALE to map the BIDS specification onto a machine readable schema.

Examples to follow as additional comments...

Links:
ancpbids: https://github.com/ANCPLabOldenburg/ancp-bids
XSD: https://www.w3.org/TR/xmlschema11-1/
Yamale: https://github.com/23andMe/Yamale

edits:

https://linkml.io (added by @yarikoptic)