isAllowed()

    boolean isAllowed(string objectClassName, string attributename)
This function returns TRUE if the attribute is listed as an allowed attribute based on the information in your slapd.oc.conf file. Otherwise, it will return FALSE. Note that this function will return false if the attrbibute is listed as required.

Example: 

$ldap = new LDAP();
$oc = "organizationalUnit";
$attribute = "businessCategory";
if ($ldap->isAllowed($oc, $attribute))
	echo "$attribute is allowed by the objectClass $oc<br>\n";
else
	echo "$attribute is not allowed by the objectClass $oc<br>\n";