All X elements below Y, but before another, descendent, Y - xslt

Question

<div n="a">
. . .
. . .
<spec>red</spec>
<div n="d">
. . .
</div>
<spec>green</spec>
. . .
<div n="b">
. . .
<spec>blue</spec>
. . .
</div>
<div n="c">
<spec>yellow</spec>
</div>
. . .
. . .
. . .
</div>
[Edited to remove the ambiguity Sean noticed. -- Thanks]
When the current element is <div n="a">, I need an XPATH expression that returns the red and green elements, but not the blue and yellow ones, as .//spec does.
When the current element is <div n="b">, the same expression needs to return the blue element; when <div n="c">, the yellow element.
Something like .//spec[but no deeper than another div if there is one]

Answer 1

In XSLT 1.0, assuming that the current node is a div:
.//spec[generate-id(current())=generate-id(ancestor::div[1])]
In XSLT 2.0 under the same assumptions:
.//spec[ancestor::div[1] is current()]
And a pure XPath 2.0 expression:
for $this in .
return
$this//spec[ancestor::div[1] is $this]
Full XSLT 1.0 transformation:
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:template match="div">
<div n="{#n}"/>
<xsl:copy-of select=
".//spec[generate-id(current())=generate-id(ancestor::div[1])]"/>
==============
<xsl:apply-templates/>
</xsl:template>
<xsl:template match="text()"/>
</xsl:stylesheet>
when applied on the provided XML document:
<div n="a">
. . .
. . .
<spec>red</spec>
<spec>green</spec>
. . .
<div n="b">
. . .
<spec>blue</spec>
. . .
</div>
<div n="c">
<spec>yellow</spec>
</div>
. . .
. . .
. . .
</div>
the wanted, correct result is produced:
<div n="a"/>
<spec>red</spec>
<spec>green</spec>
==============
<div n="b"/>
<spec>blue</spec>
==============
<div n="c"/>
<spec>yellow</spec>
==============
Full XSLT 2.0 transformation:
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:template match="div">
<div n="{#n}"/>
<xsl:sequence select=".//spec[ancestor::div[1] is current()]"/>
===================================
<xsl:apply-templates/>
</xsl:template>
<xsl:template match="text()"/>
</xsl:stylesheet>
When applied on the same XML document (above), the same correct result is produced:
<div n="a"/>
<spec>red</spec>
<spec>green</spec>
===================================
<div n="b"/>
<spec>blue</spec>
===================================
<div n="c"/>
<spec>yellow</spec>
===================================
And using pure XPath 2.0 (no current()):
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:template match="div">
<div n="{#n}"/>
<xsl:sequence select="
for $this in .
return
$this//spec[ancestor::div[1] is $this]"/>
===================================
<xsl:apply-templates/>
</xsl:template>
<xsl:template match="text()"/>
</xsl:stylesheet>
produces the same correct result:
<div n="a"/>
<spec>red</spec>
<spec>green</spec>
===================================
<div n="b"/>
<spec>blue</spec>
===================================
<div n="c"/>
<spec>yellow</spec>
===================================

Answer 2

Assuming that you are using XSLT 1.0, and you want to select `spec' children, all children, then with your desired 'current' node as the XSLT focus node, set the following variable...
<xsl:variable name="divs" select="*//div" />
Now you can select all spec descendants which are not preceded by a div descendant with this XPath expression...
//spec[not((preceding::div|ancestor::div)[count(. | $divs) = count($divs)])]
Caveat
This should work, but I have not tested it. With this caution, I leave it as an exercise to the OP to test.
Note
If you really desperately want an XPath expression that does not require you to declare an additional variable, AND you happen to be lucky enough that you already hold the current node in a node-set (lets call it $ref), the you could use this rather inefficient XPath expression...
$ref//spec[not((preceding::div|ancestor::div)[count(. | $ref/*//div) =
count( $ref/*//div) ])]
Addendum
Here is a test case that I may be referring to the comment streams.
Test Case 1 Input:
<div n="a">
<spec>red</spec>
<div n="x"/>
<spec>green</spec>
<div n="b">
<spec>blue</spec>
</div>
<div n="c">
<spec>yellow</spec>
</div>
</div>
Test Case 1 Expected output:
Should be just red