How do I update the tabstop information on a pgf

I have>        

    var  doc=app.ActiveDoc;    

                SelectElement (doc, para);      

                 var textRange = new TextRange;

                textRange.beg.obj = textRange.end.obj = para;

                textRange.beg.offset = 1;

                textRange.end.offset = Constants.FV_OBJ_END_OFFSET;

                doc.TextSelection = textRange;

                textRange = doc.TextSelection;

                var pgf = doc.TextSelection.beg.obj;

and now I need to set the tab stop New Position to a variable value, the alignment to left and the leader to .

any help appreciated, thanks!

Tracey