\startenvironment fonts_env

\starttypescript[mono] [iosevka]
  \definefontsynonym[Iosevka-Regular]    [file:iosevka-fixed-regular]
  \definefontsynonym[Iosevka-Italic]     [file:iosevka-fixed-italic]
  \definefontsynonym[Iosevka-Bold]       [file:iosevka-fixed-bold]
  \definefontsynonym[Iosevka-BoldItalic] [file:iosevka-fixed-bolditalic]
\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

\definefallbackfamily[lsrfont][math][modern][range={uppercasescript,lowercasescript}]

\starttypescript [lsrfont]
  \definetypeface [lsrfont] [rm] [serif] [palatino] [default]
  \definetypeface [lsrfont] [ss] [sans]  [heros]    [default]
  \definetypeface [lsrfont] [tt] [mono]  [modern]   [default]
  \definetypeface [lsrfont] [mm] [math]  [palatino] [default]
\stoptypescript

\stopenvironment