Create a font registry, parsing every available fonts.
Undocumented in source. Be warned that the author may not have intended to support it.
Add a font file to parse. Registers every font within that file. Important: the file must outlive the FontRegistry itself.
FontRegistry register partial font information for all fonts from the system directories, plus the ones added by the user. Aggregates all fonts by family, a bit like a browser or Word does. This allows to get one particular physical font with just a family name, an approximate weight etc. Without such font-matching, it's impractical and you need to give explicit ttf files manually.