[awestroke]

Ambigious does not mean invalid

[hinkley]

For people who see parsing as model checking, ambiguity means something vastly different (inferior) to leniency.

Fast parsers that use a schema are also doing model checking.

[chubot]

Yes, technically it means "there's more than one derivation"

But Python's pgen rejects such grammars as invalid ... The other strategy is just to pick an arbitrary interpretation