add static method
Implementation
static void add(final BuildContext ctx, final String txt, {final bool colorful = false}) {
if (_watermark != null) return;
_watermark = OverlayEntry(builder: (final _) => get(ctx, txt, colorful: colorful))
.let((final OverlayEntry entry) {
Overlay.of(ctx).insert(entry);
return entry;
});
}