a string with OpenType font features, with the syntax of the [CSS font-feature-settings property](https://www.w3.org/TR/css-fonts-4/#font-rend-desc)
the newly allocated pango.attribute.Attribute, which should be freed with pango.attribute.Attribute.destroy
Create a new font features tag attribute.
You can use this attribute to select OpenType font features like small-caps, alternative glyphs, ligatures, etc. for fonts that support them.