Sets the text of the tooltip to be markup, which is marked up with the [Pango text markup language]PangoMarkupFormat. If markup is NULL, the label will be hidden.
a markup string (see [Pango markup format]PangoMarkupFormat) or NULL
2.12
Sets the text of the tooltip to be markup, which is marked up with the [Pango text markup language]PangoMarkupFormat. If markup is NULL, the label will be hidden.