Ancestors' same-name siblings - xslt

Question

<corpus>
<header id="1">
<file>
<info>
<title id="A" />
</info>
</file>
</header>
<TEI>
<header id="2">
<file>
<info>
<title id="B" />
</info>
</file>
</header>
<header id="3">
<file>
<info>
<record>
<title id="C" />
</record>
</info>
</file>
</header>
<header id="4">
<file>
</file>
</header>
</TEI>
</corpus>
$list is a set of <title> nodes.
The depth of <title> varies, but is always somewhere under a <header>. The depth of <header> varies, but its depth from root is always the same for all nodes in a given $list.
Given a $list, I need a for-each loop that loops through headers.
When the only node in $list is title A, I need to loop only through header 1.
When the nodes in $list are titles B and C, I need to loop through headers 2, 3 and 4.

Answer 1

Use:
$list/ancestor::header[1]/../header
XSLT - based verification:
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:variable name="vList1" select=
"/*/header[1]/*/*/title"/>
<xsl:variable name="vList2" select=
"/*/TEI//title"/>
<xsl:template match="/">
<xsl:copy-of select="$vList1"/>
====
<xsl:copy-of select="$vList2"/>
====
<xsl:copy-of select=
"$vList1/ancestor::header[1]/../header"/>
====
<xsl:copy-of select=
"$vList2/ancestor::header[1]/../header"/>
</xsl:template>
</xsl:stylesheet>
when this transformation is applied on the provided XML document:
<corpus>
<header id="1">
<file>
<info>
<title id="A" />
</info>
</file>
</header>
<TEI>
<header id="2">
<file>
<info>
<title id="B" />
</info>
</file>
</header>
<header id="3">
<file>
<info>
<record>
<title id="C" />
</record>
</info>
</file>
</header>
<header id="4">
<file>
</file>
</header>
</TEI>
</corpus>
the XPath expressions are evaluated and the wanted in each case header elements are selected and output:
<title id="A"/>
====
<title id="B"/>
<title id="C"/>
====
<header id="1">
<file>
<info>
<title id="A"/>
</info>
</file>
</header>
====
<header id="2">
<file>
<info>
<title id="B"/>
</info>
</file>
</header>
<header id="3">
<file>
<info>
<record>
<title id="C"/>
</record>
</info>
</file>
</header>
<header id="4">
<file>
</file>
</header>