[xsl] XPath for expressing contiguous elements?

["Costello, Roger L. costello@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

Hi Folks,

I want an XPath expression that implements this rule:

	All <A> elements shall be contiguous within <Test>.

In this example all A's are contiguous, so the rule is satisfied:

<Test>
    <B/>
    <A/>
    <A/>
    <A/>
    <B/>
</Test>

In this example there is an intervening B, so the rule is not satisfied:

<Test>
    <B/>
    <A/>
    <A/>
    <B/>
    <A/>
    <B/>
</Test>

Below is the XPath that I created. I have two questions about it:

(1) Is it correct? Do you see anything it would fail to catch?

(2) Is there a better (simpler, more efficient) XPath expression?

Here is the XPath (within a Schematron rule):

<sch:rule context="Test">
    <sch:assert test="
        every $i in A satisfies
           (if ($i/preceding-sibling::A) then
$i/preceding-sibling::*[1][self::A] else true())
           and
           (if ($i/following-sibling::A) then
$i/following-sibling::*[1][self::A] else true())
        ">
        All A's shall be contiguous within Test.
    </sch:assert>
</sch:rule>