The filter must:

1. Delete all zero-width space characters ('\xe2\x80\x8b').
2. Replace characters form-feed ('\f') and vertical tab ('\v') for newline ('\n').
3. Delete characters carriage return ('\r').
4. Replace characters horizontal tab ('\t') for space (' ').
5. Remove white space ('\s+$') at the end.
6. Remove whitespace ('^\s+') at the beginning of the line.
7. Replace the string consisting of whitespace characters ('\n[ \r\t\v]+\n') to empty ('\n\n').