Как я могу указать межбуквенный интервал или кернинг в текстовом поле WPF?

Я бы хотел изменить интервал между символами в текстовом поле WPF.
Что-то вроде letter-spacing: 5px , доступного в CSS.
I think it is possible in XAML; what's the simplest way?

I found the "Introduction to the GlyphRun Object and Glyphs Element" document, and found it to be exceedingly unhelpful.

This is a code example from that page:

The same documentation page gives this "explanation" for what the Indices property does:

I have no idea what any of that means. I'm also not sure that Indices is the right thing - the comment in the code speaks of "character widths" which I don't care about. I want to adjust the width between characters.

Also, there is no example for how to apply a Glyphs element to a TextBox. When I tried it, my WPF test app just crashed.

What I want to do is slightly increase the empty space that appears between drawn characters within a WPF TextBox. The text will vary in length and content. Do I have to modify the Indicies property every time there is a new character? Is there a way to say "make it 20% more space than usual, for every character".

Can anybody help me?