\startenvironment env2bookk

\setuppapersize  [A5][A4]
\setuparranging  [2UP,rotated,doublesided]
\setuppagenumbering  [alternative=doublesided]
\setuplayout   [margin=0pt,width=fit]
\setupbodyfont  [lbr,12pt]

\setupheadertexts
  [][chapter]
  [\getvariable{document}{title}][]

\setuppagenumbering
  [alternative=doublesided,
   location=footer]

\unexpanded\def\MyChapterTitle#1#2%
  {\framed
    [offset=overlay,
     frame=off,
     width=\textwidth,
     align={middle,lohi}]
    {#1\blank#2}}

\setuphead
  [chapter]
  [header=high,
   command=\MyChapterTitle,
   style=\bfc,
   numberstyle=\bfb]

\setuplabeltext
  [chapter=Chapter~]


\defineconversion
    [words]
    [One, Two, Three, Four, Five]

  \definecounter [mycount]
  \setupcounter  [mycount] [numberconversion=words]

\setuphead
   [chapter]
   [header=high,
    command=\MyChapterTitle,
    style=\bfc,
    conversion=words,
    numberstyle=\bfb]


\stopenvironment