my name is Mikhail Leonov, I'm a developer on the WPF Text team.
WPF introduces a new font selection model that allows applications to select fonts using FontFamily, FontWeight, FontStyle and FontStretch properties. Customers often need to know how the information stored in the font files is mapped to these properties by the WPF engine, so we wrote a white paper that contains detailed explanation of the font mapping process in WPF. I hope this paper is useful to developers and font designers, and I'm looking forward to your feedback. The attached copy of the paper is in the PDF format, but I can also upload XPS and DOCX versions if needed.
Mikhail Leonov - MSFT