code: public int getReplaceContextLength() {
  		if (replaceContextLength == null) {
  			int replacementOffset = getReplaceRegion().getOffset();
  			ITextRegion currentRegion = getCurrentNode().getTextRegion();
  			int replaceContextLength = currentRegion.getLength() - (replacementOffset - currentRegion.getOffset());
  			this.replaceContextLength = replaceContextLength;
  			return replaceContextLength;
  		}
  		return replaceContextLength.intValue();
  	}
docs: The length of the region left to the completion offset that is part of the
  replace region.