Sets the text of tooltip to be the given string, which is marked up with the [Pango text markup language]PangoMarkupFormat. Also see gtk.tooltip.Tooltip.setMarkup.
This is a convenience property which will take care of getting the tooltip shown if the given string is not null: #GtkWidget:has-tooltip will automatically be set to true and there will be taken care of #GtkWidget::query-tooltip in the default signal handler.
Note that if both #GtkWidget:tooltip-text and #GtkWidget:tooltip-markup are set, the last one wins.
Get tooltipMarkup property.