There is also a module webforms validation<div><br></div><div><a href="https://drupal.org/project/webform_validation">https://drupal.org/project/webform_validation</a></div><div><br></div><div><br><br>Op dinsdag 27 mei 2014 heeft Afan Pasalic &lt;<a href="mailto:drupal@afan.net">drupal@afan.net</a>&gt; het volgende geschreven:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi,<br>
This time I didn’t do anything embarrassing. :-)<br>
<br>
How can I extend an existing module? E.g. I want to add some features/validations in web form module. I know I MUST NOT change the code in the webform module itself.<br>
I believe there is some solution to extend a module. Something like extending a theme (sub-theme).  And updating the module will not break the website.<br>
--<br>
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</blockquote></div>