Label.setMarkup

Parses str which is marked up with the [Pango text markup language]PangoMarkupFormat, setting the label’s text and attribute list based on the parse results.

If the str is external data, you may need to escape it with glib.global.markupEscapeText or glib.global.markupPrintfEscaped:

GtkWidget *label = gtk_label_new (NULL);
const char *str = "some text";
const char *format = "<span style=\"italic\">\%s</span>";
char *markup;

markup = g_markup_printf_escaped (format, str);
gtk_label_set_markup (GTK_LABEL (label), markup);
g_free (markup);

This function will set the #GtkLabel:use-markup property to true as a side effect.

If you set the label contents using the #GtkLabel:label property you should also ensure that you set the #GtkLabel:use-markup property accordingly.

See also: gtk.label.Label.setText