Use of an undeclared constant

in interwiki.module there is the following line:

$form[interwiki]['intro'] = array('#type' => 'markup', '#value' => "<p>$output</p>");

which should be written:

$form['interwiki']['intro'] = array('#type' => 'markup', '#value' => "<p>$output</p>");

Actually, undeclared constants have the value of a string containing the constant name, but that behavior can change in future. Or it can have a collateral effect if a module defines the interwiki constant.