> Can you provide some intuition on which languages can be parsed by this algorithm, and which can't?

The restriction is that any recursion in the grammar has to be inside explicit begin and end tokens. For example, you can't write a rule like

    stmt = 'if' expr 'then' stmt* | expr

because `stmt` refers to itself directly, but

    stmt = [ 'if' expr 'then' stmt* 'end' ] | expr

is OK -- the [ and ] symbols indicate explicit recursion using 'if' and 'end' as the begin and end tokens.[1]

> Btw, why did you choose the name Owl?

I wanted a bird name, and Owl was short and easy to type!

. . .

[1] Though in this case, the language is still visibly pushdown, since you can expand it manually to:

    stmt = (('if' expr 'then')+ expr*)+ | expr

This is because the grammar only has right recursion. Middle recursion (like you get if you add an 'else' clause) can't be expanded like this, so explicit recursion is necessary to parse languages which use it.

To automate this expansion process (and re-association into a sensible parse tree), Owl also has syntax for operators with precedence. Here's an example: https://ianh.github.io/owl/try/#expr