Function make 

pub(crate) fn make(
    sources: &[PathBuf],
    limit: u64,
    advised: u32,
    folder: &Path,
) -> (Vec<Attached>, Vec<Left>)

The media chosen (sources, in their order) made fit for one message under limit bytes (decisions 6 to 10), written into folder: those that go, and those that do not and why. advised: the carrier’s largest picture’s long side (0 none). The room is the message’s own measure with its media empty, to the longest number, with the words’ reserve (room_for). Only regular files are read; each picture is decoded once, by its own format’s reader.