How to set a new FontFamily to my egui app?

Question

So i tried the Examples in egui documentation and it works. However the Examples in the egui documentation, seems to focus on overwriting the existing FontFamily (Proportional,Monospace):

let mut fonts = FontDefinitions::default();

// Install my own font (maybe supporting non-latin characters):
fonts.font_data.insert("my_font".to_owned(),
   FontData::from_static(include_bytes!("../../fonts/Ubuntu-Light.ttf"))); // .ttf and .otf supported

// Put my font first (highest priority):
fonts.families.get_mut(&FontFamily::Proportional).unwrap()
    .insert(0, "my_font".to_owned());

// Put my font as last fallback for monospace:
fonts.families.get_mut(&FontFamily::Monospace).unwrap()
    .push("my_font".to_owned());

egui_ctx.set_fonts(fonts);

But how to i declare or define a completely new Family in the Enum?

pub enum FontFamily {
    Proportional,
    Monospace,
    Name(Arc<str>),
}

pub enum FontFamily {
    Proportional,
    Monospace,
    my_font, <-- How i put the font here as a new FamilyMember? 
    Name(Arc<str>),
}

I would like to use my own my_font only for specfic labels or fields like in this case:

   ui.add(
            egui::TextEdit::singleline(&mut ss)
            .text_color(egui::Color32::LIGHT_RED)
            .font(egui::FontSelection::FontId(FontId::new(
            20.,
            egui::FontFamily::my_font, <--
            ))),