Code:
<input type="text" name="somefield1" size="40" tabindex="1">
<input type="text" name="somefield2" size="40" tabindex="3">
<input type="text" name="somefield3" size="40" tabindex="2">
<input type="text" name="somefield4" size="40" tabindex="4">
Hitting tab would move in this order:
somefield1, somefield3, somefield2, somefield4.