anchor.diff:  assert documentationSupport ->
     doxygen != null
     && graphviz != null;
  -assert eventGUISupport ->
  +assert debugGUISupport ->
     cairo != null
     && glib != null
     && gtk3 != null;
  
positive.code: , documentationSupport ? false
    , doxygen ? null
    , graphviz ? null
   # GUI event viewer support
  , eventGUISupport ? false
    , cairo ? null
    , glib ? null
    , gtk3 ? null
  
negative.code: 
    configureFlags = [
      "--${boolEn documentationSupport}-documentation"
      "--${boolEn debugGUISupport}-debug-gui"
      "--${boolEn testsSupport}-tests"
    ];
  
  