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XSLT stylesheet to convert cmark XML back to Commonmark
Initial version of an XSLT stylesheet that converts the XML format produced by `cmark -t xml` back to Commonmark. Fixes commonmark#264
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‎tools/xml2md.xsl

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<?xml version="1.0" encoding="UTF-8"?>
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<!--
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xml2md.xsl
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==========
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This XSLT stylesheet transforms the cmark XML format back to Commonmark.
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Since the XML output is lossy, a lossless MD->XML->MD roundtrip isn't
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possible. The XML->MD->XML roundtrip should produce the original XML,
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though.
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HTML blocks and inlines aren't supported.
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Example usage with xsltproc:
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cmark -t xml doc.md | xsltproc -novalid xml2md.xsl -
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-->
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<xsl:stylesheet
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version="1.0"
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xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
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xmlns:md="http://commonmark.org/xml/1.0">
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<xsl:output method="text" encoding="utf-8"/>
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<!-- Generic templates -->
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<xsl:template match="/ | md:document | md:list">
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<xsl:apply-templates select="md:*"/>
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</xsl:template>
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<xsl:template match="md:*">
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<xsl:message>Unsupported element '<xsl:value-of select="local-name()"/>'</xsl:message>
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</xsl:template>
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<xsl:template match="md:*" mode="indent"/>
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<!-- Indent blocks -->
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<xsl:template match="md:*" mode="indent-block">
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<xsl:if test="preceding-sibling::md:*">
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<xsl:if test="not(ancestor::md:list[1][@tight='true'])">
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<xsl:apply-templates select="ancestor::md:*" mode="indent"/>
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<xsl:text>&#10;</xsl:text>
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</xsl:if>
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<xsl:apply-templates select="ancestor::md:*" mode="indent"/>
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</xsl:if>
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</xsl:template>
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<!-- Heading -->
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<xsl:template match="md:heading">
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<xsl:apply-templates select="." mode="indent-block"/>
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<xsl:value-of select="substring('###### ', 7 - @level)"/>
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<xsl:apply-templates select="md:*"/>
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<xsl:text>&#10;</xsl:text>
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</xsl:template>
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<!-- Paragraph -->
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<xsl:template match="md:paragraph">
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<xsl:apply-templates select="." mode="indent-block"/>
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<xsl:apply-templates select="md:*"/>
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<xsl:text>&#10;</xsl:text>
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</xsl:template>
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<!-- Thematic break -->
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<xsl:template match="md:thematic_break">
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<xsl:apply-templates select="." mode="indent-block"/>
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<xsl:text>***&#10;</xsl:text>
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</xsl:template>
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<!-- List -->
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<xsl:template match="md:list">
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<xsl:apply-templates select="." mode="indent-block"/>
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<xsl:apply-templates select="md:*"/>
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</xsl:template>
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<xsl:template match="md:item">
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<xsl:apply-templates select="." mode="indent-block"/>
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<xsl:choose>
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<xsl:when test="../@type = 'bullet'">-</xsl:when>
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<xsl:when test="../@type = 'ordered'">
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<xsl:value-of select="../@start + position() - 1"/>
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<xsl:choose>
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<xsl:when test="../@delim = 'period'">.</xsl:when>
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<xsl:when test="../@delim = 'paren'">)</xsl:when>
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</xsl:choose>
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</xsl:when>
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</xsl:choose>
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<xsl:text> </xsl:text>
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<xsl:apply-templates select="md:*"/>
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</xsl:template>
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<xsl:template match="md:item" mode="indent">
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<xsl:choose>
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<xsl:when test="../@type = 'bullet'">
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<xsl:text> </xsl:text>
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</xsl:when>
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<xsl:when test="../@type = 'ordered'">
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<xsl:text> </xsl:text>
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</xsl:when>
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</xsl:choose>
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</xsl:template>
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<!-- Block quote -->
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<xsl:template match="md:block_quote">
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<xsl:apply-templates select="." mode="indent-block"/>
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<xsl:text>&gt; </xsl:text>
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<xsl:apply-templates select="md:*"/>
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</xsl:template>
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<xsl:template match="md:block_quote" mode="indent">
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<xsl:text>&gt; </xsl:text>
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</xsl:template>
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<!-- Code block -->
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<xsl:template match="md:code_block">
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<xsl:apply-templates select="." mode="indent-block"/>
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<!-- TODO: Longer delimiter if text contains ``` -->
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<xsl:text>```</xsl:text>
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<xsl:value-of select="@info"/>
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<xsl:text>&#10;</xsl:text>
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<xsl:call-template name="indent-lines">
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<xsl:with-param name="code" select="."/>
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</xsl:call-template>
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<xsl:apply-templates select="ancestor::md:*" mode="indent"/>
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<xsl:text>```</xsl:text>
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<xsl:text>&#10;</xsl:text>
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</xsl:template>
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<!-- Inline HTML -->
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<xsl:template match="md:html_block">
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<xsl:apply-templates select="." mode="indent-block"/>
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<xsl:value-of select="substring-before(., '&#10;')"/>
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<xsl:text>&#10;</xsl:text>
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<xsl:call-template name="indent-lines">
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<xsl:with-param name="code" select="substring-after(., '&#10;')"/>
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</xsl:call-template>
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</xsl:template>
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<!-- Indent multiple lines -->
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<xsl:template name="indent-lines">
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<xsl:param name="code"/>
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<xsl:if test="contains($code, '&#10;')">
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<xsl:apply-templates select="ancestor::md:*" mode="indent"/>
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<xsl:value-of select="substring-before($code, '&#10;')"/>
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<xsl:text>&#10;</xsl:text>
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<xsl:call-template name="indent-lines">
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<xsl:with-param name="code" select="substring-after($code, '&#10;')"/>
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</xsl:call-template>
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</xsl:if>
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</xsl:template>
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<!-- Text -->
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<xsl:template match="md:text">
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<xsl:variable name="t" select="string(.)"/>
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<xsl:variable name="first" select="substring($t, 1, 1)"/>
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<xsl:variable name="marker-check" select="translate(substring($t, 1, 10), '0123456789', '')"/>
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<xsl:choose>
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<!-- Escape ordered list markers -->
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<xsl:when test="starts-with($marker-check, '.') and $first != '.'">
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<xsl:value-of select="substring-before($t, '.')"/>
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<xsl:text>\.</xsl:text>
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<xsl:call-template name="escape-text">
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<xsl:with-param name="text" select="substring-after($t, '.')"/>
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</xsl:call-template>
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</xsl:when>
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<xsl:when test="starts-with($marker-check, ')') and $first != ')'">
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<xsl:value-of select="substring-before($t, ')')"/>
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<xsl:text>\)</xsl:text>
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<xsl:call-template name="escape-text">
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<xsl:with-param name="text" select="substring-after($t, ')')"/>
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</xsl:call-template>
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</xsl:when>
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<!-- Escape leading block characters -->
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<xsl:when test="contains('-+>#=~', $first)">
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<xsl:text>\</xsl:text>
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<xsl:value-of select="$first"/>
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<xsl:call-template name="escape-text">
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<xsl:with-param name="text" select="substring($t, 2)"/>
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</xsl:call-template>
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</xsl:when>
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<!-- Otherwise -->
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<xsl:otherwise>
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<xsl:call-template name="escape-text">
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<xsl:with-param name="text" select="$t"/>
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</xsl:call-template>
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</xsl:otherwise>
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</xsl:choose>
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</xsl:template>
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<!-- Breaks -->
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<xsl:template match="md:softbreak">
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<xsl:text>&#10;</xsl:text>
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<xsl:apply-templates select="ancestor::md:*" mode="indent"/>
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</xsl:template>
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<xsl:template match="md:linebreak">
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<xsl:text> &#10;</xsl:text>
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<xsl:apply-templates select="ancestor::md:*" mode="indent"/>
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</xsl:template>
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<!-- Emphasis -->
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<xsl:template match="md:emph">
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<xsl:text>*</xsl:text>
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<xsl:apply-templates select="md:*"/>
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<xsl:text>*</xsl:text>
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</xsl:template>
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<xsl:template match="md:strong">
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<xsl:text>**</xsl:text>
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<xsl:apply-templates select="md:*"/>
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<xsl:text>**</xsl:text>
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</xsl:template>
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<!-- Inline code -->
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<xsl:template match="md:code">
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<xsl:call-template name="escape-code">
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<xsl:with-param name="text" select="string(.)"/>
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</xsl:call-template>
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</xsl:template>
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<xsl:template name="escape-code">
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<xsl:param name="text"/>
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<xsl:param name="delim" select="'`'"/>
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<xsl:choose>
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<xsl:when test="contains($text, $delim)">
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<xsl:call-template name="escape-code">
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<xsl:with-param name="text" select="$text"/>
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<xsl:with-param name="delim" select="concat($delim, '`')"/>
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</xsl:call-template>
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</xsl:when>
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<xsl:otherwise>
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<xsl:value-of select="$delim"/>
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<xsl:value-of select="$text"/>
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<xsl:value-of select="$delim"/>
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</xsl:otherwise>
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</xsl:choose>
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</xsl:template>
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<!-- Links and images -->
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<xsl:template match="md:link | md:image">
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<xsl:if test="self::md:image">!</xsl:if>
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<xsl:text>[</xsl:text>
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<xsl:apply-templates select="md:*"/>
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<xsl:text>](</xsl:text>
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<xsl:call-template name="escape-text">
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<xsl:with-param name="text" select="string(@destination)"/>
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<xsl:with-param name="escape" select="'()'"/>
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</xsl:call-template>
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<xsl:if test="string(@title)">
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<xsl:text> "</xsl:text>
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<xsl:call-template name="escape-text">
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<xsl:with-param name="text" select="string(@title)"/>
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<xsl:with-param name="escape" select="'&quot;'"/>
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</xsl:call-template>
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<xsl:text>"</xsl:text>
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</xsl:if>
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<xsl:text>)</xsl:text>
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</xsl:template>
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<!-- Inline HTML -->
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<xsl:template match="md:html_inline">
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<xsl:value-of select="."/>
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</xsl:template>
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<!-- Escape text -->
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<xsl:template name="escape-text">
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<xsl:param name="text"/>
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<xsl:param name="escape" select="'*_`&lt;[]&amp;'"/>
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<xsl:variable name="trans" select="translate($text, $escape, '\\\\\\\')"/>
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<xsl:choose>
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<xsl:when test="contains($trans, '\')">
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<xsl:variable name="safe" select="substring-before($trans, '\')"/>
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<xsl:variable name="l" select="string-length($safe)"/>
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<xsl:value-of select="$safe"/>
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<xsl:text>\</xsl:text>
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<xsl:value-of select="substring($text, $l + 1, 1)"/>
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<xsl:call-template name="escape-text">
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<xsl:with-param name="text" select="substring($text, $l + 2)"/>
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<xsl:with-param name="escape" select="$escape"/>
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</xsl:call-template>
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</xsl:when>
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<xsl:otherwise>
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<xsl:value-of select="$text"/>
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</xsl:otherwise>
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</xsl:choose>
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</xsl:template>
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</xsl:stylesheet>

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