There has been a request in the RSTA forums to allow line numbering in RTextScrollPane to start at an arbitrary number, e.g. "4" instead of "1".
Changes have been committed to SVN, revision 109.
The following code will make the first line displayed be numbered "5":
RTextScrollPane sp = new RTextScrollPane(...);
Gutter gutter = sp.getGutter();
Let me know if there are problems. It'll be in the next release.
Added in 1.3.4.