Readme specification of keys is ambiguous

[vmchale]

In the readme, it specifies bare keys as follows:

Bare keys may only contain letters, numbers, underscores, and dashes `(A-Za-z0-9_-)`

This can be confusing, because, for example,

çe = "value"

is not considered valid TOML though I expected it to be.

If possible, you should either:

1. Avoid specifying letters as (A-Za-z) and instead specify letters as "unicode letters and unicode nonspacing marks (to include dependent vowels such as བོ) and numbers as "unicode decimal digists".
2. Specify that letters and numerals should be valid ASCII and that they may not be letters or numerals from utf8.

Thanks!

[dtolnay]

Based on #283 and #337 it seems like the restriction to A-Za-z0-9_- is very intentional. I agree that "letter" is not the clearest way to specify A-Za-z, "number" is not the clearest way to specify 0-9, and "dash" is not the clearest way to specify -.

Relevant PR on the Rust side: toml-rs/toml-rs#177

[ChristianSi]

Yes, the restriction is intentional. It would probably be better to rewrite the above as:

Bare keys may only contain ASCII letters, ASCII digits, underscores, and hyphens (A-Za-z0-9_-).

[mk-pmb]

Yes, "ASCII letter" is a better wording, especially considering that

letters and numerals should be valid ASCII and that they may not be letters or numerals from utf8.

is useless because there would be no letters left, as ASCII is a proper subset of UTF-8.