Allow extra parameters when splicing

[nmattia]

It would be nice to be able to write the following:

<div class="a-class" {...dynAttrs}> ... </div>

It could be done such that in the above case a-class would have priority over a class defined by dynAttrs whereas in

<div {...dynAttrs} class="a-class"> ... </div>

a class defined by dynAttrs would take over.