[Meir]

Thank you Stefan!

OK, now my first ever JavaScript macro is complete (bug reports are welcomed) :

/*
  This eeJavaScript macro will toggle a selected string through the
  sequence of lower case -> capitalize -> uppercase -> lower case again.
  If no string is selected, the word where the cursor is will.
  The starting state is a function of the "first" and "next" characters.
  * If both characters are upper, the string will be converted be lower.
  * If only the first character is upper, the string will be converted
    to upper.
  * If neither the first character nor the next are upper case, the
    string will be capitalyzed.
  A single character will toggle just between lower and upper case.
*/
s = document.selection.Text;
if( document.selection.IsEmpty ){
   document.selection.SelectWord();
   s = document.selection.Text;
    }
f = s.charCodeAt(0);
n = s.charCodeAt(1);

if( (f >= 0x41 && f <= 0x5a && s.length == 1)
                 ||
    (f >= 0x41 && f <= 0x5a && n >= 0x41 && n <= 0x5a)){
    document.selection.ChangeCase(eeCaseLowerCase);
    }
else if( f >= 0x41 && f <= 0x5a ){
    document.selection.ChangeCase(eeCaseUpperCase);
    }
else {
    document.selection.ChangeCase(eeCaseCapitalize);
    }

Regards,
Meir