I think the word "understable" should be "understandable" in http://codex.wordpress.org/WordPress_Features
under the section:
Cruft-free Permalinks
The URLs for all the pages in your weblog can be made to conform to a standard, cruft-free system, and all the links are structured, sensible, and "understable" to human and machines, and that includes search engines. Clean URLs are essential for search engine optimization and an improved user experience.
