Focus event

[3dfx]

Hello!

I am trying to make a script which validates if a radio button is
checked and if it is not displays the radio button in red (as if it is
on focus).
Would you please give me a hint how can I force the radio button to
behave like if it is on focus? I can bring the focus to a particular
button with javascript but this is not a solution, because only one
element can be on focus at a time...

Thanks!