Function opt_cfws_colon_opt_cfws 

pub(crate) fn opt_cfws_colon_opt_cfws(
    input: &[u8],
) -> Option<ParsedItem<'_, ()>>

Available on crate feature parsing only.

Equivalent to opt(cfws), ascii_char::<b':'>, and opt(cfws) called in sequence, but is better optimized for the common case where no cfws is present.