gtk:expander-use-underline (object)

object -- a gtk:expander widget
use-underline -- true if underlines in the text indicate mnemonics

The accessor for the use-underline slot of the gtk:expander class returns whether an embedded underline in the expander label indicates a mnemonic. If true, an underline in the text of the expander label indicates the next character should be used for the mnemonic accelerator key.