Register fonts

旺文社国語辞典 uses its font’s italic form for the variable x.
Register a font, then select its internal family name in your stylesheet.
Register a font
dictionary.add_font("Birds.otf", mkd.Buffer.map("Birds.otf"))
auto font = MKD::RetainedSpan::map("Birds.otf").value();
dictionary.addFont("Birds.otf", font.span()).value();
The writer stores the font under fonts/ and registers its filename in product
metadata. Use .ttf, .otf or .ttc with a matching signature. Font filenames
must be unique across the product.
Select the registered font by its internal family or PostScript name, which may
differ from the filename. For a font named Birds:
body { font-family: Birds; }
Read back registered fonts through media and fonts.
Include any required font license in the product.
Next: Style articles.