[OU] MIME-type for locally-populated windows

[Fred Bone]

Code of the following type:

    var doc = window.open("output.html", "output").document;
    doc.open("text/plain");
    doc.writeln("This should be plain text");
    doc.writeln("This should be on the second line");
    doc.close();

apparently causes IE and Firefox to associate a MIME-type of "text/plain" 
with the contents being placed in the new window, thus giving the 
"obvious" result of two lines of text. Opera, however (and, I'm told, 
Safari) will apparently ignore the MIME-type parameter to the doc.open 
call, treating the contents as text/html and so running-on the intended 
two lines into one.

Is this functionality likely to appear in Opera any time soon? Is there 
another (better?) way to achieve the intended result?