Function features 

pub(crate) fn features(
    card: &Card,
    auth: Option<&AuthResults>,
    internal_date: Option<i64>,
    links: &[String],
) -> [f32; 35]

The header features of a message: its card (headers, parts, text), its authentication results (auth_results, or the corpus’s own checks), when its provider received it (IMAP’s INTERNALDATE, the Maildir file’s time), the domains of its links (tokenize::tokens). A value it cannot know is f32::NAN (see the module).