applying fcode to a text range?

Hi all,

I'm trying to apply an fcode to a text range.

If I manually select text, this code makes the text bold:

fcodes = new Array();

fcodes[0] = FCodes.TXT_BOLD;

Fcodes(fcodes);

However, if I try to programmatically select the text, the fcode has no effect:

var tr = new TextRange (); 

tr.beg.obj = tr.end.obj = pgf; 

tr.beg.offset = 0; 

tr.end.offset = 5;

fcodes = new Array();

fcodes[0] = FCodes.TXT_BOLD;

Fcodes(fcodes);

I fear I'm missing something simple or obvious. Must my code explicitly toggle the text range as "selected"?

-Alan