not(*[not(self::A)][following-sibling::A][preceding-sibling::A])

returns true if and only if there is no non-A element that is both preceded
and followed by an A element, which I think is equivalent to your expression
and rather simpler.

Michael Kay
Saxonica


> On 1 May 2017, at 14:00, Costello, Roger L. costello@xxxxxxxxx
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> 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>