895 lines
24 KiB
HTML
895 lines
24 KiB
HTML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
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"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
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<head>
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<meta http-equiv="Content-Type" content="application/xhtml+xml; charset=UTF-8" />
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<meta name="generator" content="AsciiDoc 10.2.0" />
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<title>gitformat-chunk(5)</title>
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<style type="text/css">
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/* Shared CSS for AsciiDoc xhtml11 and html5 backends */
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/* Default font. */
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body {
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font-family: Georgia,serif;
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}
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/* Title font. */
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h1, h2, h3, h4, h5, h6,
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div.title, caption.title,
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thead, p.table.header,
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#toctitle,
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#author, #revnumber, #revdate, #revremark,
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#footer {
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font-family: Arial,Helvetica,sans-serif;
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}
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body {
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margin: 1em 5% 1em 5%;
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}
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a {
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color: blue;
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text-decoration: underline;
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}
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a:visited {
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color: fuchsia;
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}
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em {
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font-style: italic;
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color: navy;
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}
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strong {
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font-weight: bold;
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color: #083194;
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}
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h1, h2, h3, h4, h5, h6 {
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color: #527bbd;
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margin-top: 1.2em;
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margin-bottom: 0.5em;
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line-height: 1.3;
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}
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h1, h2, h3 {
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border-bottom: 2px solid silver;
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}
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h2 {
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padding-top: 0.5em;
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}
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h3 {
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float: left;
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}
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h3 + * {
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clear: left;
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}
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h5 {
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font-size: 1.0em;
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}
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div.sectionbody {
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margin-left: 0;
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}
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hr {
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border: 1px solid silver;
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}
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p {
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margin-top: 0.5em;
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margin-bottom: 0.5em;
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}
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ul, ol, li > p {
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margin-top: 0;
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}
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ul > li { color: #aaa; }
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ul > li > * { color: black; }
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.monospaced, code, pre {
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font-family: "Courier New", Courier, monospace;
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font-size: inherit;
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color: navy;
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padding: 0;
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margin: 0;
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}
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pre {
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white-space: pre-wrap;
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}
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#author {
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color: #527bbd;
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font-weight: bold;
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font-size: 1.1em;
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}
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#email {
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}
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#revnumber, #revdate, #revremark {
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}
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#footer {
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font-size: small;
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border-top: 2px solid silver;
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padding-top: 0.5em;
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margin-top: 4.0em;
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}
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#footer-text {
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float: left;
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padding-bottom: 0.5em;
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}
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#footer-badges {
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float: right;
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padding-bottom: 0.5em;
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}
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#preamble {
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margin-top: 1.5em;
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margin-bottom: 1.5em;
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}
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div.imageblock, div.exampleblock, div.verseblock,
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div.quoteblock, div.literalblock, div.listingblock, div.sidebarblock,
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div.admonitionblock {
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margin-top: 1.0em;
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margin-bottom: 1.5em;
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}
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div.admonitionblock {
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margin-top: 2.0em;
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margin-bottom: 2.0em;
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margin-right: 10%;
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color: #606060;
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}
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div.content { /* Block element content. */
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padding: 0;
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}
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/* Block element titles. */
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div.title, caption.title {
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color: #527bbd;
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font-weight: bold;
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text-align: left;
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margin-top: 1.0em;
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margin-bottom: 0.5em;
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}
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div.title + * {
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margin-top: 0;
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}
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td div.title:first-child {
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margin-top: 0.0em;
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}
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div.content div.title:first-child {
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margin-top: 0.0em;
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}
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div.content + div.title {
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margin-top: 0.0em;
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}
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div.sidebarblock > div.content {
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background: #ffffee;
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border: 1px solid #dddddd;
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border-left: 4px solid #f0f0f0;
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padding: 0.5em;
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}
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div.listingblock > div.content {
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border: 1px solid #dddddd;
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border-left: 5px solid #f0f0f0;
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background: #f8f8f8;
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padding: 0.5em;
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}
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div.quoteblock, div.verseblock {
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padding-left: 1.0em;
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margin-left: 1.0em;
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margin-right: 10%;
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border-left: 5px solid #f0f0f0;
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color: #888;
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}
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div.quoteblock > div.attribution {
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padding-top: 0.5em;
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text-align: right;
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}
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div.verseblock > pre.content {
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font-family: inherit;
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font-size: inherit;
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}
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div.verseblock > div.attribution {
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padding-top: 0.75em;
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text-align: left;
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}
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/* DEPRECATED: Pre version 8.2.7 verse style literal block. */
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div.verseblock + div.attribution {
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text-align: left;
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}
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div.admonitionblock .icon {
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vertical-align: top;
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font-size: 1.1em;
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font-weight: bold;
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text-decoration: underline;
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color: #527bbd;
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padding-right: 0.5em;
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}
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div.admonitionblock td.content {
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padding-left: 0.5em;
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border-left: 3px solid #dddddd;
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}
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div.exampleblock > div.content {
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border-left: 3px solid #dddddd;
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padding-left: 0.5em;
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}
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div.imageblock div.content { padding-left: 0; }
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span.image img { border-style: none; vertical-align: text-bottom; }
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a.image:visited { color: white; }
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dl {
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margin-top: 0.8em;
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margin-bottom: 0.8em;
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}
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dt {
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margin-top: 0.5em;
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margin-bottom: 0;
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font-style: normal;
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color: navy;
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}
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dd > *:first-child {
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margin-top: 0.1em;
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}
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ul, ol {
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list-style-position: outside;
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}
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ol.arabic {
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list-style-type: decimal;
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}
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ol.loweralpha {
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list-style-type: lower-alpha;
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}
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ol.upperalpha {
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list-style-type: upper-alpha;
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}
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ol.lowerroman {
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list-style-type: lower-roman;
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}
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ol.upperroman {
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list-style-type: upper-roman;
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}
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div.compact ul, div.compact ol,
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div.compact p, div.compact p,
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div.compact div, div.compact div {
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margin-top: 0.1em;
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margin-bottom: 0.1em;
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}
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tfoot {
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font-weight: bold;
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}
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td > div.verse {
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white-space: pre;
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}
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div.hdlist {
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margin-top: 0.8em;
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margin-bottom: 0.8em;
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}
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div.hdlist tr {
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padding-bottom: 15px;
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}
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dt.hdlist1.strong, td.hdlist1.strong {
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font-weight: bold;
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}
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td.hdlist1 {
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vertical-align: top;
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font-style: normal;
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padding-right: 0.8em;
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color: navy;
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}
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td.hdlist2 {
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vertical-align: top;
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}
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div.hdlist.compact tr {
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margin: 0;
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padding-bottom: 0;
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}
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.comment {
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background: yellow;
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}
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.footnote, .footnoteref {
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font-size: 0.8em;
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}
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span.footnote, span.footnoteref {
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vertical-align: super;
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}
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#footnotes {
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margin: 20px 0 20px 0;
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padding: 7px 0 0 0;
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}
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#footnotes div.footnote {
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margin: 0 0 5px 0;
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}
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#footnotes hr {
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border: none;
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border-top: 1px solid silver;
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height: 1px;
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text-align: left;
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margin-left: 0;
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width: 20%;
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min-width: 100px;
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}
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div.colist td {
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padding-right: 0.5em;
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padding-bottom: 0.3em;
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vertical-align: top;
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}
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div.colist td img {
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margin-top: 0.3em;
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}
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@media print {
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#footer-badges { display: none; }
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}
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#toc {
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margin-bottom: 2.5em;
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}
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#toctitle {
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color: #527bbd;
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font-size: 1.1em;
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font-weight: bold;
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margin-top: 1.0em;
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margin-bottom: 0.1em;
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}
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div.toclevel0, div.toclevel1, div.toclevel2, div.toclevel3, div.toclevel4 {
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margin-top: 0;
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margin-bottom: 0;
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}
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div.toclevel2 {
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margin-left: 2em;
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font-size: 0.9em;
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}
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div.toclevel3 {
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margin-left: 4em;
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font-size: 0.9em;
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}
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div.toclevel4 {
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margin-left: 6em;
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font-size: 0.9em;
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}
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span.aqua { color: aqua; }
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span.black { color: black; }
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span.blue { color: blue; }
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span.fuchsia { color: fuchsia; }
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span.gray { color: gray; }
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span.green { color: green; }
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span.lime { color: lime; }
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span.maroon { color: maroon; }
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span.navy { color: navy; }
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span.olive { color: olive; }
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span.purple { color: purple; }
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span.red { color: red; }
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span.silver { color: silver; }
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span.teal { color: teal; }
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span.white { color: white; }
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span.yellow { color: yellow; }
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span.aqua-background { background: aqua; }
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span.black-background { background: black; }
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span.blue-background { background: blue; }
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span.fuchsia-background { background: fuchsia; }
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span.gray-background { background: gray; }
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span.green-background { background: green; }
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span.lime-background { background: lime; }
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span.maroon-background { background: maroon; }
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span.navy-background { background: navy; }
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span.olive-background { background: olive; }
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span.purple-background { background: purple; }
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span.red-background { background: red; }
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span.silver-background { background: silver; }
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span.teal-background { background: teal; }
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span.white-background { background: white; }
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span.yellow-background { background: yellow; }
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span.big { font-size: 2em; }
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span.small { font-size: 0.6em; }
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span.underline { text-decoration: underline; }
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span.overline { text-decoration: overline; }
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span.line-through { text-decoration: line-through; }
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div.unbreakable { page-break-inside: avoid; }
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/*
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* xhtml11 specific
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*
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* */
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div.tableblock {
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margin-top: 1.0em;
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margin-bottom: 1.5em;
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}
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div.tableblock > table {
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border: 3px solid #527bbd;
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}
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thead, p.table.header {
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font-weight: bold;
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color: #527bbd;
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}
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p.table {
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margin-top: 0;
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}
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/* Because the table frame attribute is overridden by CSS in most browsers. */
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div.tableblock > table[frame="void"] {
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border-style: none;
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}
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div.tableblock > table[frame="hsides"] {
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border-left-style: none;
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border-right-style: none;
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}
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div.tableblock > table[frame="vsides"] {
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border-top-style: none;
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border-bottom-style: none;
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}
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/*
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* html5 specific
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*
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* */
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table.tableblock {
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margin-top: 1.0em;
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margin-bottom: 1.5em;
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}
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thead, p.tableblock.header {
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font-weight: bold;
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color: #527bbd;
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}
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p.tableblock {
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margin-top: 0;
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}
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table.tableblock {
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border-width: 3px;
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border-spacing: 0px;
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border-style: solid;
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border-color: #527bbd;
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border-collapse: collapse;
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}
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th.tableblock, td.tableblock {
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border-width: 1px;
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padding: 4px;
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border-style: solid;
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border-color: #527bbd;
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}
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table.tableblock.frame-topbot {
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border-left-style: hidden;
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border-right-style: hidden;
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}
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table.tableblock.frame-sides {
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border-top-style: hidden;
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border-bottom-style: hidden;
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}
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table.tableblock.frame-none {
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border-style: hidden;
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}
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th.tableblock.halign-left, td.tableblock.halign-left {
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text-align: left;
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}
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th.tableblock.halign-center, td.tableblock.halign-center {
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text-align: center;
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}
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th.tableblock.halign-right, td.tableblock.halign-right {
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text-align: right;
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}
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th.tableblock.valign-top, td.tableblock.valign-top {
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vertical-align: top;
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}
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th.tableblock.valign-middle, td.tableblock.valign-middle {
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vertical-align: middle;
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}
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th.tableblock.valign-bottom, td.tableblock.valign-bottom {
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vertical-align: bottom;
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}
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|
|
|
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/*
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* manpage specific
|
|
*
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* */
|
|
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body.manpage h1 {
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padding-top: 0.5em;
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padding-bottom: 0.5em;
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border-top: 2px solid silver;
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border-bottom: 2px solid silver;
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}
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|
body.manpage h2 {
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border-style: none;
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}
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body.manpage div.sectionbody {
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margin-left: 3em;
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}
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@media print {
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body.manpage div#toc { display: none; }
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}
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|
|
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</style>
|
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<script type="text/javascript">
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/*<+'])');
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// Function that scans the DOM tree for header elements (the DOM2
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|
// nodeIterator API would be a better technique but not supported by all
|
|
// browsers).
|
|
var iterate = function (el) {
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|
for (var i = el.firstChild; i != null; i = i.nextSibling) {
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if (i.nodeType == 1 /* Node.ELEMENT_NODE */) {
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var mo = re.exec(i.tagName);
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if (mo && (i.getAttribute("class") || i.getAttribute("className")) != "float") {
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result[result.length] = new TocEntry(i, getText(i), mo[1]-1);
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}
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iterate(i);
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}
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}
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}
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iterate(el);
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return result;
|
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}
|
|
|
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var toc = document.getElementById("toc");
|
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if (!toc) {
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return;
|
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}
|
|
|
|
// Delete existing TOC entries in case we're reloading the TOC.
|
|
var tocEntriesToRemove = [];
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var i;
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for (i = 0; i < toc.childNodes.length; i++) {
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var entry = toc.childNodes[i];
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|
if (entry.nodeName.toLowerCase() == 'div'
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&& entry.getAttribute("class")
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&& entry.getAttribute("class").match(/^toclevel/))
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tocEntriesToRemove.push(entry);
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}
|
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for (i = 0; i < tocEntriesToRemove.length; i++) {
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toc.removeChild(tocEntriesToRemove[i]);
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}
|
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|
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// Rebuild TOC entries.
|
|
var entries = tocEntries(document.getElementById("content"), toclevels);
|
|
for (var i = 0; i < entries.length; ++i) {
|
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var entry = entries[i];
|
|
if (entry.element.id == "")
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|
entry.element.id = "_toc_" + i;
|
|
var a = document.createElement("a");
|
|
a.href = "#" + entry.element.id;
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// Footnotes generator
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/////////////////////////////////////////////////////////////////////
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/* Based on footnote generation code from:
|
|
* http://www.brandspankingnew.net/archive/2005/07/format_footnote.html
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*/
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footnotes: function () {
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// Because JavaScript has no s (dotall) regex flag.
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note = spans[i].innerHTML.match(/\s*\[([\s\S]*)]\s*/)[1];
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spans[i].innerHTML =
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"[<a id='_footnoteref_" + n + "' href='#_footnote_" + n +
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"' title='View footnote' class='footnote'>" + n + "</a>]";
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spans[i].setAttribute("data-note", note);
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noteholder.innerHTML +=
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"<div class='footnote' id='_footnote_" + n + "'>" +
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"<a href='#_footnoteref_" + n + "' title='Return to text'>" +
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n + "</a>. " + note + "</div>";
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"[<a href='#_footnote_" + n +
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"' title='View footnote' class='footnote'>" + n + "</a>]";
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var timerId;
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asciidoc.footnotes();
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asciidoc.install();
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/*]]>*/
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|
</script>
|
|
</head>
|
|
<body class="manpage">
|
|
<div id="header">
|
|
<h1>
|
|
gitformat-chunk(5) Manual Page
|
|
</h1>
|
|
<h2>NAME</h2>
|
|
<div class="sectionbody">
|
|
<p>gitformat-chunk -
|
|
Chunk-based file formats
|
|
</p>
|
|
</div>
|
|
</div>
|
|
<div id="content">
|
|
<div class="sect1">
|
|
<h2 id="_synopsis">SYNOPSIS</h2>
|
|
<div class="sectionbody">
|
|
<div class="paragraph"><p>Used by <a href="gitformat-commit-graph.html">gitformat-commit-graph(5)</a> and the "MIDX" format (see
|
|
the pack format documentation in <a href="gitformat-pack.html">gitformat-pack(5)</a>).</p></div>
|
|
</div>
|
|
</div>
|
|
<div class="sect1">
|
|
<h2 id="_description">DESCRIPTION</h2>
|
|
<div class="sectionbody">
|
|
<div class="paragraph"><p>Some file formats in Git use a common concept of "chunks" to describe
|
|
sections of the file. This allows structured access to a large file by
|
|
scanning a small "table of contents" for the remaining data. This common
|
|
format is used by the <code>commit-graph</code> and <code>multi-pack-index</code> files. See
|
|
the <code>multi-pack-index</code> format in <a href="gitformat-pack.html">gitformat-pack(5)</a> and
|
|
the <code>commit-graph</code> format in <a href="gitformat-commit-graph.html">gitformat-commit-graph(5)</a> for
|
|
how they use the chunks to describe structured data.</p></div>
|
|
<div class="paragraph"><p>A chunk-based file format begins with some header information custom to
|
|
that format. That header should include enough information to identify
|
|
the file type, format version, and number of chunks in the file. From this
|
|
information, that file can determine the start of the chunk-based region.</p></div>
|
|
<div class="paragraph"><p>The chunk-based region starts with a table of contents describing where
|
|
each chunk starts and ends. This consists of (C+1) rows of 12 bytes each,
|
|
where C is the number of chunks. Consider the following table:</p></div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre><code>| Chunk ID (4 bytes) | Chunk Offset (8 bytes) |
|
|
|--------------------|------------------------|
|
|
| ID[0] | OFFSET[0] |
|
|
| ... | ... |
|
|
| ID[C] | OFFSET[C] |
|
|
| 0x0000 | OFFSET[C+1] |</code></pre>
|
|
</div></div>
|
|
<div class="paragraph"><p>Each row consists of a 4-byte chunk identifier (ID) and an 8-byte offset.
|
|
Each integer is stored in network-byte order.</p></div>
|
|
<div class="paragraph"><p>The chunk identifier <code>ID</code>[<code>i</code>] is a label for the data stored within this
|
|
file from <code>OFFSET</code>[<code>i</code>] (inclusive) to <code>OFFSET</code>[<code>i+1</code>] (exclusive). Thus, the
|
|
size of the <code>i</code>`th <code>chunk</code> <code>is</code> <code>equal</code> <code>to</code> <code>the</code> <code>difference</code> <code>between</code> `OFFSET[<code>i+1</code>]
|
|
and <code>OFFSET</code>[<code>i</code>]. This requires that the chunk data appears contiguously
|
|
in the same order as the table of contents.</p></div>
|
|
<div class="paragraph"><p>The final entry in the table of contents must be four zero bytes. This
|
|
confirms that the table of contents is ending and provides the offset for
|
|
the end of the chunk-based data.</p></div>
|
|
<div class="paragraph"><p>Note: The chunk-based format expects that the file contains <em>at least</em> a
|
|
trailing hash after <code>OFFSET</code>[<code>C+1</code>].</p></div>
|
|
<div class="paragraph"><p>Functions for working with chunk-based file formats are declared in
|
|
<code>chunk-format.h</code>. Using these methods provide extra checks that assist
|
|
developers when creating new file formats.</p></div>
|
|
</div>
|
|
</div>
|
|
<div class="sect1">
|
|
<h2 id="_writing_chunk_based_file_formats">Writing chunk-based file formats</h2>
|
|
<div class="sectionbody">
|
|
<div class="paragraph"><p>To write a chunk-based file format, create a <code>struct</code> <code>chunkfile</code> by
|
|
calling <code>init_chunkfile</code>() and pass a <code>struct</code> <code>hashfile</code> pointer. The
|
|
caller is responsible for opening the <code>hashfile</code> and writing header
|
|
information so the file format is identifiable before the chunk-based
|
|
format begins.</p></div>
|
|
<div class="paragraph"><p>Then, call <code>add_chunk</code>() for each chunk that is intended for writing. This
|
|
populates the <code>chunkfile</code> with information about the order and size of
|
|
each chunk to write. Provide a <code>chunk_write_fn</code> function pointer to
|
|
perform the write of the chunk data upon request.</p></div>
|
|
<div class="paragraph"><p>Call <code>write_chunkfile</code>() to write the table of contents to the <code>hashfile</code>
|
|
followed by each of the chunks. This will verify that each chunk wrote
|
|
the expected amount of data so the table of contents is correct.</p></div>
|
|
<div class="paragraph"><p>Finally, call <code>free_chunkfile</code>() to clear the <code>struct</code> <code>chunkfile</code> data. The
|
|
caller is responsible for finalizing the <code>hashfile</code> by writing the trailing
|
|
hash and closing the file.</p></div>
|
|
</div>
|
|
</div>
|
|
<div class="sect1">
|
|
<h2 id="_reading_chunk_based_file_formats">Reading chunk-based file formats</h2>
|
|
<div class="sectionbody">
|
|
<div class="paragraph"><p>To read a chunk-based file format, the file must be opened as a
|
|
memory-mapped region. The chunk-format API expects that the entire file
|
|
is mapped as a contiguous memory region.</p></div>
|
|
<div class="paragraph"><p>Initialize a <code>struct</code> <code>chunkfile</code> pointer with <code>init_chunkfile</code>(<code>NULL</code>).</p></div>
|
|
<div class="paragraph"><p>After reading the header information from the beginning of the file,
|
|
including the chunk count, call <code>read_table_of_contents</code>() to populate
|
|
the <code>struct</code> <code>chunkfile</code> with the list of chunks, their offsets, and their
|
|
sizes.</p></div>
|
|
<div class="paragraph"><p>Extract the data information for each chunk using <code>pair_chunk</code>() or
|
|
<code>read_chunk</code>():</p></div>
|
|
<div class="ulist"><ul>
|
|
<li>
|
|
<p>
|
|
<code>pair_chunk</code>() assigns a given pointer with the location inside the
|
|
memory-mapped file corresponding to that chunk’s offset. If the chunk
|
|
does not exist, then the pointer is not modified.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
<code>read_chunk</code>() takes a <code>chunk_read_fn</code> function pointer and calls it
|
|
with the appropriate initial pointer and size information. The function
|
|
is not called if the chunk does not exist. Use this method to read chunks
|
|
if you need to perform immediate parsing or if you need to execute logic
|
|
based on the size of the chunk.
|
|
</p>
|
|
</li>
|
|
</ul></div>
|
|
<div class="paragraph"><p>After calling these methods, call <code>free_chunkfile</code>() to clear the
|
|
<code>struct</code> <code>chunkfile</code> data. This will not close the memory-mapped region.
|
|
Callers are expected to own that data for the timeframe the pointers into
|
|
the region are needed.</p></div>
|
|
</div>
|
|
</div>
|
|
<div class="sect1">
|
|
<h2 id="_examples">Examples</h2>
|
|
<div class="sectionbody">
|
|
<div class="paragraph"><p>These file formats use the chunk-format API, and can be used as examples
|
|
for future formats:</p></div>
|
|
<div class="ulist"><ul>
|
|
<li>
|
|
<p>
|
|
<strong>commit-graph:</strong> see <code>write_commit_graph_file</code>() and <code>parse_commit_graph</code>()
|
|
in <code>commit-graph.c</code> for how the chunk-format API is used to write and
|
|
parse the commit-graph file format documented in
|
|
the commit-graph file format in <a href="gitformat-commit-graph.html">gitformat-commit-graph(5)</a>.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
<strong>multi-pack-index:</strong> see <code>write_midx_internal</code>() and <code>load_multi_pack_index</code>()
|
|
in <code>midx.c</code> for how the chunk-format API is used to write and
|
|
parse the multi-pack-index file format documented in
|
|
the multi-pack-index file format section of <a href="gitformat-pack.html">gitformat-pack(5)</a>.
|
|
</p>
|
|
</li>
|
|
</ul></div>
|
|
</div>
|
|
</div>
|
|
<div class="sect1">
|
|
<h2 id="_git">GIT</h2>
|
|
<div class="sectionbody">
|
|
<div class="paragraph"><p>Part of the <a href="git.html">git(1)</a> suite</p></div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div id="footnotes"><hr /></div>
|
|
<div id="footer">
|
|
<div id="footer-text">
|
|
Last updated
|
|
2025-08-18 02:18:23 CEST
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html>
|