Best way to warn a user of potentially bad data

Question

I have a web page with an autocomplete enabled combo textbox/dropdown. The user is able to enter values manually or pick a value from the list. While free text input is acceptable, I would like to visually warn the user that the data they have manually entered does not match a value in the list.

For reasons related to page layout I would like to avoid displaying anything on the page itself - the warning must be something that floats around. That being said, there are a few specific questions that I have:

• Where should the warning message appear? Above the textbox? Below?
• What should the warning message say? "The data you have entered does not match any listed values"?
• Should the warning message disappear on it's own after X seconds, or should the user have to click it?

Answer 1

The way I read it the free input will filter a list dynamically as the user types. In the case that a user enters something that doesn't match any of the items that are being filtered then the appropriate place to notify of this is where the user currently has their focus, namely where the filtered results are listed.

Simply switch out the list of possible autocomplete results for a label explaining that the current input doesn't match any item. That way the user will be notified of this right away, without moving focus from the filter control, in contrast to popping up a message on the side/top/bottom outside the control which will force the user to switch focus.

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