[XBL] Clarification: white space nodes

In my opinion, the influence of the white space nodes on the content
elements should be made clear in the spec. Consider the following two 
XML samples where p is a bound element.

<p><a/></p>

and

<p>
   <a/>
</p>

The explicit children of the p elements are different. The first <p> has 
only <a>, but the second one has <textnode>, <a>, and <textnode>. If the 
<a> element is included into the shadow tree through includes attribute, 
the next content element will be replaced either with the white spaces 
or with its own content depending on the used markup.

That may confuse authors since they usually use the white spaces to 
clarify the markup. I think it should be mentioned that the white spaces 
in the bound element's markup may affect to the shadow tree.

Mikko