Why doesn't a <table>'s margin collapse with an adjacent <p>?

Question

From my understanding of the CSS spec, a table above or below a paragraph should collapse vertical margins with it. However, that's not happening here:

table {
  margin: 100px;
  border: solid red 2px;
}
p {
  margin: 100px
}

<table>
  <tr>
    <td>
      This is a one-celled table with 100px margin all around.
    </td>
  </tr>
</table>

<p>This is a paragraph with 100px margin all around.</p>

I thought there would be 100px between the two elements, but there are 200px -- the margins aren't collapsing.

Why not?

Edit: It appears to be the table's fault: if I duplicate the table and duplicate the paragraph, the two paragraphs will collapse margins. The two tables won't. And, as noted above, a table won't collapse margins with a paragraph. Is this compliant behaviour?

table {
  margin: 100px;
  border: solid red 2px;
}

<table>
  <tr>
    <td>
      This is a one-celled table with 100px margin all around.
    </td>
  </tr>
</table>
<table>
  <tr>
    <td>
      This is a one-celled table with 100px margin all around.
    </td>
  </tr>
</table>

p {
  margin: 100px
}

<p>This is a paragraph with 100px margin all around.</p>
<p>This is a paragraph with 100px margin all around.</p>

Answer 1

Margin collapsing is only defined for block elements. Try it - add display: block to the table styles, and suddenly it works (and alters the display of the table...)

Tables are special. In the CSS specs, they're not quite block elements - special rules apply to size and position, both of their children (obviously), and of the table element itself.

Relevant specs:

http://www.w3.org/TR/CSS21/box.html#collapsing-margins
http://www.w3.org/TR/CSS21/visuren.html#block-box