One of the things I put a lot of work into for Spelling Plus Library was architecting it in a very modular, extendable fashion. The main reason for this was to allow developers to use it in the way that makes most sense for their projects. For example, Buzzword only uses the SpellingDictionary class, which handles all of the spell checking and spelling suggestion logic, and the WordListLoader, but manages the user interface themselves.

A secondary benefit is that many of the classes are very useful on their own. The best example of this is the TextHighlighter class that forms the core of the SPL SpellingHighlighter. It is a very powerful class for finding and highlighting words in a text field in real time.

It includes a ton of features, including support for manual selections, multi-line highlights, smart targeting, autoupdating on change and scroll, interactive highlights, and more. It will be gaining even more functionality in the upcoming 1.1 release of SPL.

Here is a simple demo of the TextHighlighter class in action. Less than 10 lines of code. It shows how you could use TextHighlighter to search for and highlight words in a text field. You can edit and scroll the text area, and the highlights will update in real time.

This sample will be included with the 1.1 update of SPL.

I've considered licensing TextHighlighter separately from SPL, but I'm not sure if anyone would be interested. Let me know if you are.