If a form control causes something to happen when a user tabs into it, this could be confusing for people with cognitive disabilities or people using assistive technologies, such as screen readers or screen magnifiers. For example, if a form is automatically submitted once all forms have been completed, this may not be expected by the user. Similarly, if changing the option in a drop-down select box causes something to change without explicitly being actioned by the user, this may cause them confusion.
Ensure that any change of context that is caused by a form (e.g. a change of language or submission of a form) is only triggered by a specific action, such as pressing a submit button or clicking on a link.
//This is an example of how a form control should not be used. The form is submitted when the selected option is changed. There is no submit button for the user to press
<form id="language_selection" action="submit.php" method="post">
<select name="lang" onchange="lang.submit();">
<option>English</option>
<option>French</option>
<option>German</option>
<option>Arabic</option>
</select>
</form>