There is not a Max Selected message that can be set, however one can write a script to do it. Here is my way of handling it
Names Default To Here( 1 );
New Window( "Example",
cb = Check Box(
{"One", "Two", "Three"},
curSelected = cb << get selected;
If( N Items( curSelected ) > 2,
// Determine the one just selected
For( i = 1, i <= N Items( cb << get items ), i++,
If(
Contains( curSelected, (cb << get items)[i] ) > 0 &
Contains( prevSelected, (cb << get items)[i] ) == 0,
dialog("Too many selections");
cb << set(i,0);
Break();
)
);
,
prevSelected = curSelected;
);
)
);
Jim