The tweak-action property of type g:action (Read)
A toggle action that can be used to switch to the tweak page of the font
chooser widget, which lets the user tweak the OpenType features and variation
axes of the selected font. The action will be enabled or disabled depending on whether the selected font has any features or axes.
Details
The gtk:font-chooser-widget widget lists the available fonts,
styles and sizes, allowing the user to select a font. It is used in the gtk:font-chooser-dialog widget to provide a dialog
for selecting fonts.