Function parse_excluded_dates 

pub fn parse_excluded_dates(
    raw: &str,
    on_rejected: impl FnMut(&str),
) -> Vec<String>

The dates listed in an EXDATE value, normalised to YYYY-MM-DD.

Separators are commas and whitespace, in any mix — a list is written for a person to read, and both are what people write. The result keeps the order the value was written in and holds one entry per date, whichever way the value spelled it.

A field that does not parse as a date is handed to on_rejected as it is met rather than collected: the value is only as short as the file makes it, and one written entirely of rubbish would otherwise be held twice over — once in the file, once in a vector — for a caller that reports the first few and drops the rest.