Function assisted_formula_edit 

fn assisted_formula_edit(
    ui: &mut Ui,
    model: &Model,
    text: &mut String,
    id: Id,
    hint: &str,
    span: Option<Range<usize>>,
    from: usize,
) -> Response

A formula editor with autocomplete (crate::completion): while a name is typed (at or after byte from), a list of what may complete it drops under the edit (Up/Down select, Tab or Enter accept, Esc closes; a click accepts too), the rest of the selected name and its parameters trail the caret in light gray, and a tooltip shows the signature of the function being completed or called, the current argument in bold. With the list closed every key reaches the edit, so Enter still commits.