Macro font_face_descriptors

macro_rules! font_face_descriptors {
    (
        mandatory descriptors = [
            $( #[$m_doc: meta] $m_name: tt $m_ident: ident / $m_gecko_ident: ident: $m_ty: ty, )*
        ]
        optional descriptors = [
            $( #[$o_doc: meta] $o_name: tt $o_ident: ident / $o_gecko_ident: ident: $o_ty: ty, )*
        ]
    ) => { ... };
}