What's the syntax when entering input checks
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It is used to validate user inputs.

so for example if I wanted the users to enter only a range of zipcodes would I do this:
00000-10452 or 00001, 00002,00003 ....10452.

you have to have the zipcode table to verify the user input

In ProfileFields table row "zip" column "Check"
return ( zipcode_check($arg0) );

add this function to inc/design.inc.php
function zipcode_check($zip)
{
$zip = strip_tags($zip);
$res = (int)db_value("SELECT `ZIPCode` FROM `ZIPCodes` where `ZIPCode`=trim('$zip')");
if ( $res )
return true;
else
return false;
}