if((!isset($error)) and (!ereg("^[_0-9a-z]*$",$nicker))) $error="The nickname needs to be composed of letters, numbers and underscores ";
This means both must be judged, not just one, so using and and or are used to judge only one condition.
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This means both must be judged, not just one, so using and and or are used to judge only one condition.