int rangeLimit = fColorer.currentLimit();
AttributeMap style = fColorer.currentStyle();
if (oldText.characterStyleLimit(rangeStart) < rangeLimit ||
oldText.characterStyleAt(rangeStart) != style) {
int cstart = rangeStart-start;
int climit = rangeLimit-start;
if (newText == null) {
newText = new StyledText(oldText, start, limit);