Legend (in order): deleted text, inserted text, ▶ block move mark, moved block, single character changes, highlighted moved block and ◀ block mark, and ambiguous insertion aligned to line.
wikEd diff is a free JavaScript visual diff library for inline text comparisons. It is the only available JavaScript diff library that detects and highlights block moves and that works on the word and character level. While wikEd diff has been developed and optimized for comparing Wikipedia source texts, it works great for any type of text, including program code. The library is customizable, has Unicode and multilingual support, is fully commented and documented, and is free (public domain). The script is used by the Wikipedia/MediaWiki in-browser editor wikEd and by the gadget wikEdDiff. You can test the library by checking any of these gadgets in your English Wikipedia preferences. For easy text comparisons by copy-and-pasting you can also use the wikEd diff online tool and demo. The library has also been ported to PHP in the form of a MediaWiki extension.