If I have a form with such code:
<form action="" method="post" onsubmit="return validationFunction();">

Or a such link:
<a href="http://example.com" onclick="return someFunction();">test</a>

Validator marks the code as error:
Bad value return validationFunction(); for attribute onsubmit on element form: invalid return

Bad value return someFunction(); for attribute onclick on element a: invalid return