\starttypescript[mono] [iosevka]
  \definefontsynonym[Iosevka-Regular]    [name:iosevkaymhgmedium]
  \definefontsynonym[Iosevka-Italic]     [name:iosevkaymhgmediumitalic]
  \definefontsynonym[Iosevka-Bold]       [name:iosevkaymhgbold]
  \definefontsynonym[Iosevka-BoldItalic] [name:iosevkaymhgbolditalic]
\stoptypescript

\starttypescript[mono] [iosevka]
  \setups[font:fallback:mono]
  \definefontsynonym[Mono]           [Iosevka-Regular]    [features=default]
  \definefontsynonym[MonoItalic]     [Iosevka-Italic]     [features=default]
  \definefontsynonym[MonoBold]       [Iosevka-Bold]       [features=default]
  \definefontsynonym[MonoBoldItalic] [Iosevka-BoldItalic] [features=default]
\stoptypescript

\starttypescript [ymhgd]
  \definetypeface [ymhgd] [rm] [serif] [libertinus] [default] [rscale=1.73]
  \definetypeface [ymhgd] [ss] [sans]  [lato] [default] [rscale=1.73]
  \definetypeface [ymhgd] [tt] [mono]  [iosevka]    [default] [rscale=1.55]
  \definetypeface [ymhgd] [mm] [math]  [libertinus] [default] [rscale=1.73]
\stoptypescript