}
public static void alterTag(ISweaveTag swtold, ISweaveTag swtnew) {
startMergedUndo();
addMergedUndo(new RemoveSweaveTagUndoableEdit(swtold));
rmTagFromObjMan(swtold);
removeText(swtold.getLatexPos(), swtold.getSweaveString().length());
addMergedUndo(new AddSweaveTagUndoableEdit(swtnew));
insertText( swtnew.getSpacers()[0] + swtnew.getSweaveString() + swtnew.getSpacers()[1],
swtnew.getLatexStartWithSpacers());