Warn on complex natural language doctypes

[lagru]

The current grammar allows nesting of natural language constructs such as tuple of ..., (N, 3) array, dict of {...: ...}. This can quickly lead to doctypes that are actually more confusing to read. I currently see two solutions to this:

• Disallow in grammar I could rewrite the grammar in a way that only allows natural language constructs in simple contexts and without nesting. However, this requires a more complex grammar and some duplication.

• Warn I'd prefer to find a solution that warns users that they might want to improve the readability of the expression. Maybe that can be integrated with DoctypeTransformer.