Function strip_certainty 

pub fn strip_certainty(
    written: &str,
) -> Result<(IntegerType, Option<Certainty>)>

A written number with its certainty taken off it: music21’s Date._stripError. Only one symbol is expected, and the first one met is the one read. A fraction is read as the whole number before the point – music21 drops milliseconds on purpose.

Errors

Something that is not a number at all.