Unexpected letter when a letter is expected (among others)

[ip1981]

A simple string a-1] fails to parse saying that "a" is unexpected, while expected [, whitespaces, letter or digit, -, .. The "a" letter fits "letter or digit".

P. S. It also says the error is at position 3.

[jgrund]

The error for this expression looks like:

Err(
    Errors {
        position: 3,
        errors: [
            Expected(
                Token(
                    '[',
                ),
            ),
            Expected(
                Static(
                    "whitespaces",
                ),
            ),
            Expected(
                Static(
                    "letter or digit",
                ),
            ),
            Expected(
                Token(
                    '-',
                ),
            ),
            Expected(
                Token(
                    '.',
                ),
            ),
            Unexpected(
                Token(
                    'a',
                ),
            ),
        ],
    },
)

Everything except the unexpected token a looks correct.