Allow extra parameters when splicing

It would be nice to be able to write the following:

``` html
<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

``` html
<div {...dynAttrs} class="a-class"> ... </div>
```

a class defined by `dynAttrs` would take over.
