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copied!<p>Here’s the hierarchy for dealing with user errors or warnings, applied to validating user input to a field.</p> <ol> <li><p>Remove the element that may result in an error. Do you really need the user’s birth date? Can you get by just as well with something else that won’t require validation, such as option buttons for “Under 18 years old,” and “18 or over”?</p></li> <li><p>Prevent the error. Make it impossible to enter invalid input in the first place. For example, use a dropdown list, or “picture” the field, refusing any unacceptable characters (e.g., letters for a phone number).</p></li> <li><p>Accept the input and possibly correct it automatically and echoing the result back to the user. Make <em>something</em> out of the input. If the user types 4--14#008 for a date, auto-correct it to be April 14 2008. If the format doesn’t match a version number, check if it’s a Release Number and lookup the corresponding Version number. If it doesn’t fit your idea of a valid address, well, just assume that it is (maybe it’s for a foreign country). Does it really matter if the user’s birth date mangled?</p></li> <li><p>Provide Undo, not verification, showing clearly the implications of what the user did and providing a clear path to reverse it. When the user enters the number of stock shares to trade, show the dollar value beside it, in case the user confused shares with dollars. Keep the fields editable so the user can fix it.</p></li> <li><p>Provide warning and error text in the primary window or web page itself; text should be apparent without being disorienting, non-modal, and disappear automatically when the error is corrected. When a unrecognized date is entered, underline it in red and put text beside it saying “unrecognized date,” perhaps including a Help link for more information.</p></li> <li><p>Modal message box.</p></li> </ol>

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