\startenvironment fonts_env

\starttypescript[mono] [iosevka]
  \definefontsynonym[Iosevka-Regular]    [name:iosevkaslabmedium]
  \definefontsynonym[Iosevka-Italic]     [name:iosevkaslabmediumitalic]
  \definefontsynonym[Iosevka-Bold]       [name:iosevkaslabbold]
  \definefontsynonym[Iosevka-BoldItalic] [name:iosevkaslabbolditalic]
\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 [lsrfont]
  \definetypeface [lsrfont] [rm] [serif] [libertinus] [default]
  \definetypeface [lsrfont] [ss] [sans]  [libertinus] [default]
  \definetypeface [lsrfont] [tt] [mono]  [iosevka]    [default] [rscale=0.85]
  \definetypeface [lsrfont] [mm] [math]  [libertinus] [default]
\stoptypescript

\stopenvironment