/usr/share/epiphany-browser/epiphany-bookmarks-html.xsl is in epiphany-browser-data 3.18.5-0ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 | <?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:purl="http://purl.org/rss/1.0/"
  xmlns:dc="http://purl.org/dc/elements/1.1/"
  xmlns:ephy="http://gnome.org/ns/epiphany#"
  exclude-result-prefixes="dc purl rdf">
<!--
Copyright © 2004 Stefan Rotsch
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
$Id$
-->
<xsl:output method="html" encoding="UTF-8" indent="yes" />
<!-- Create a key assigning an item's topic to each item -->
<xsl:key name="topics" match="purl:item" use="dc:subject" />
<xsl:template match="rdf:RDF">
    <!-- Generate DTD -->
    <xsl:text disable-output-escaping="yes"><![CDATA[<!DOCTYPE NETSCAPE-Bookmark-file-1>]]>
</xsl:text>
    <!-- Page header and title -->
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
    <title>Bookmarks</title>
    <h1>Bookmarks</h1>
    <dl>
    <!-- Items with Topics assigned will be processed first -->
    <xsl:for-each select="purl:item/dc:subject[count(.. | key('topics', .)[1]) = 1]">
        <xsl:sort select="." />
        <dt><h3><xsl:value-of select="." /></h3><dl>
        <xsl:for-each select="key('topics', .)">
            <xsl:sort select="purl:title" />
                <!-- Use smart link URIs if they exist, see bug #534565 -->
                <xsl:choose>
                    <xsl:when test="ephy:smartlink">
                        <dt><a href="{./ephy:smartlink}"><xsl:value-of select="./purl:title" /></a></dt>
                    </xsl:when>
                    <xsl:otherwise>
                        <dt><a href="{./purl:link}"><xsl:value-of select="./purl:title" /></a></dt>
                    </xsl:otherwise>
                </xsl:choose>
        </xsl:for-each>
        <!-- Force a linebreak; otherwise thinks will break for Topics with only 1 item -->
        <xsl:text>
        </xsl:text>
        </dl></dt>
    </xsl:for-each>
    <!-- Now Bookmarks without topics will be added at the bottom of the output file -->
    <xsl:for-each select="purl:item">
        <xsl:sort select="./purl:title" />
            <xsl:if test="not(dc:subject)">
                <!-- Use smart link URIs if they exist, see bug #534565 -->
                <xsl:choose>
                    <xsl:when test="ephy:smartlink">
                        <dt><a href="{./ephy:smartlink}"><xsl:value-of select="./purl:title" /></a></dt>
                    </xsl:when>
                    <xsl:otherwise>
                        <dt><a href="{./purl:link}"><xsl:value-of select="./purl:title" /></a></dt>
                    </xsl:otherwise>
                </xsl:choose>
            </xsl:if>
    </xsl:for-each>
    <!-- Closing tag of outer dl -->
    </dl>
</xsl:template>
</xsl:stylesheet>
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