\setupinteraction
  [title=TITLE,
    subtitle=SUBTITLE,
    author=AUTHOR,
    keyword={{KEYWORD1, KEYWORD2}, KEYWORD3}]

\setupbackend
  [format={pdf/ua-1},
%    profile=srgb.icc, % can't validate PDF/A-3, so this only blows up the PDF
%    intent={ISO Coated v2 300\letterpercent\space (ECI)},
    level=0]

\setuptagging[state=start] % should be set automatically, if 'tagging = true'

\setuplanguage[en]

% DisplayDocTitle key is not set to true
%
% [from PDFUA-Reference-09_(English-invoice).pdf]
% 129 0 obj
% <</Type/Catalog/Pages 1 0 R/ViewerPreferences<</DisplayDocTitle true>>/PageMode/UseOutlines/Outlines 43 0 R/Lang(en)/StructTreeRoot 2 0 R/MarkInfo<</Marked true/Suspects false>>/OutputIntents[ 128 0 R]/Metadata 127 0 R>>
% endobj
% this may interfer with other ViewerPreferences settings?

\startluacode
    lpdf.addtocatalog("ViewerPreferences",lpdf.dictionary{DisplayDocTitle = true})
\stopluacode

\def\tag#1{\quote{\tt#1}}

\starttext
  Warning: This document may contain errors and traces of hazelnuts.

  \blank[big]

  \startMPcode
    fill fullcircle scaled 3cm withcolor red;
  \stopMPcode

  \blank[big]

  The \quote{Matterhorn Protocol} gives a condensed overview of the possible failure conditions
  and the used structure types (p.4).\par

\stoptext