Function from_the_open 

pub fn from_the_open(
    left_out: &[(FileFormat, usize)],
    lake: Option<&str>,
    files_differ: Disagreement,
    names_look_like_data: bool,
) -> Vec<Note>

What the open itself has to say, before a footer has been read.

Two facts, both decided by the route that opened the directory rather than by anything in the data: which of the directory’s data files this read passed over, and whether the directory is a lake table being read as its plain files. Neither is a defect in the data — they are what datui chose to do, and #275’s rule is that datui never refuses a read the user asked for and always says what it did instead.