Function attach_plain_tooltip 

pub fn attach_plain_tooltip(
    ctx: &mut BuildContext<'_>,
    anchor_id: WidgetId,
    text: impl Into<LocalizedString>,
    delay: Duration,
) -> WidgetId

Attach a plain tooltip — first tier, a single line of text.

The one door for plain tooltips, and the reason it exists rather than each widget doing ctx.add(TooltipWidget::new(text)) inline: the body is built the first time a dwell matures over the anchor, not on every rebuild of it. A plain tip is cheap on its own, but it is attached to nearly every control in the framework, so on a data view’s row delegate the framework was paying for one per control per row per rebuild — and paying again to tear them all down, which is where the time actually went.