UI Patterns and Techniques

Forgiving Format

From http://wunderground.com
Use when:	Your UI can accept input of various kinds from the user -- different meanings, different formats, etc. -- but you don't want to clutter up the UI with a bunch of separate text fields to "type this OR that OR that OR...".
Why:	The user just wants to get something done, not think about complicated either-or choices and fiddly UIs. Computers are good at figuring out how to handle input of different types (up to a point, anyway). It's a perfect match: let the user type whatever they need, and if it's reasonable, make the software do the right thing with it. This can help simplify the UI tremendously. It may even remove the requirement for an Input Hint, though they're often seen together.
How:	The catch (you knew there would be one): It turns a UI design problem into a programming problem. You have to think about what kinds of stuff a user is likely to type in -- maybe you're asking for a date or time, and the variation will just be in the format. That's an easy case. Or maybe you're asking for search terms, and the variation will be in what the software does with the data. That's harder. Can the software disambiguate one case from another? How? Each case is unique. Just make sure that the software's response to various input parameters matches what users expect it to do. Test, test, and test again with real users.