I have not received your email address yet. Using a perl script or bbfind is not really anything to do with FoldingText but this command is a simple example using bbfind from terminal (or bbedit worksheet) which will return all lines for each document with these tags excluding done.
bbfind -g '@(due|high|hold|idea|inprogress|monthly|todo|waiting)(?>(?!@done).)*$' "/Users/username/Documents" --gui
If you add --gui at end of the line then it will display in BBEdit window which makes ir clearer to see the results and to navigate each occurrence.