[VE][108] Ther is no attribute onclick

Error [108]: "there is no attribute X"

I'm using xhtml transitional 1.0 and i have a form which i want to validate
via javascript. so i have my submit button:

<input type="submit" id="botao" onClick="javascript: return
ValidaLogin();" value="Entrar" class="bt" />


Then w3c says there is no attribute onClick. so how do I validate my form??

And it also says there is no attribute onKeyDown which I use in my textboxes
for if i have more than one button on my page, I use the keydown event so
that when the user hits enter, I activate the click of the right button for
the textbox he is in.
If I can't use onKeyDown, how do I do this??