Function splitter 

pub fn splitter(
    ui: &mut Ui<'_>,
    label: &str,
    dir: Dir,
    thickness: f32,
    tag: impl Into<Value>,
) -> Key

A divider between two panes that the pointer drags: thickness px across, growing along the rest of its parent, in the theme’s border colour and its accent while hovered or held, with the resize arrows, and tag as its on_drag. dir is the parent’s: in a Dir::Row the panes sit side by side and the bar stands between them; in a Dir::Column it lies across. A press on it leaves the keyboard where it was (keep_focus), as a divider beside an editor should.

The split is the app’s: ev.drag() on the tag’s event, and Drag::ratio() is the pointer’s place across the parent — .x for a row’s split, .y for a column’s — which is the new fraction as it is. Returns the bar’s key.