The contents of the label.
If the string contains Pango markup (see [[email protected]_markup]), you will have to set the [[email protected]:use-markup] property to true in order for the label to display the markup attributes. See also [[email protected]_markup] for a convenience function that sets both this property and the [[email protected]:use-markup] property at the same time.
If the string contains underlines acting as mnemonics, you will have to set the [[email protected]:use-underline] property to true in order for the label to display them.