Nested accordion with not selector works, but I can't figure out why!

Nested accordion with not selector works, but I can't figure out why!

1) I built a nested accordion using the dt (definition term) of a dd (definition list) as the header.


<dl class="accordion">
      <dt>Term</dt>
      <dd>Description 
            <dl class="accordion">
                  <dt>Term</dt>
                  <dd>Description</dd>
            </dl>
      </dd>
</dl>


  $(".accordion").accordion({ 
      header: "dt",
       heightStyle: "content",
       active: false,
       collapsible: true
  });

2) I found that clicking on the child (nested) accordion closed the parent, so I looked around for a fix and found this jsfiddle:

<div class="accordion">
    <h3>Home</h3>
    <div class="accordion">
        <h3>Sub-Div1</h3>
        <div>
            <p>This is a sub-div</p>
        </div>
        <h3>Sub-Div2</h3>
        <div>
            <p>This is a sub-div</p>
        </div>
    </div>
</div>

    $(".accordion").accordion({
        header: "> h3:not(.item)",
        heightStyle: "content",
        active: false,
        collapsible: true
    });


3) I adapted the jsfiddle jquery to my 'dt' selector:

  $(".accordion").accordion({ 
      header: "> dt:not(.item)",
      collapsible: true,
      heightStyle: "content"
  }); 

And it worked!

But I can't figure out how it works. I'm especially perturbed by the '.item'. That looks like a class but the class isn't present in either the jsfiddle html or my html.

I tried taking '.item' out of the jquery on the jsfiddle and it completely broke the accordions.
I changed the '.item' to '.xxxxitem' and it worked again.

There was a difference when I tested taking out '.item' on my own web page - the accordions worked perfectly, so:

on JSfiddle these both worked:

header: "> h3:not(.item)"
header: "> h3:not(.xxxxxitem)"

but this didn't:

header: "> h3:not()"

whereas on my own web site all three options (substituting 'h3' with 'dt') worked.

Could anyone shed some light on this for me?

Chris