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<!DOCTYPE reference PUBLIC "-//OASIS//DTD DITA Reference//EN" "reference.dtd">
<!--  This file is part of the DITA Open Toolkit project. See the accompanying LICENSE file for applicable license.  -->
<reference id="code-reference">

  <title>Extended codeblock processing</title>

  <titlealts>
    <navtitle>Codeblock extensions</navtitle>
  </titlealts>

  <shortdesc>DITA-OT provides additional processing support beyond that which is mandated by the DITA specification.
    These extensions can be used to define character encodings or line ranges for code references, normalize
    indentation, add line numbers or display whitespace characters in code blocks.</shortdesc>
  <prolog>
    <metadata>
      <keywords>
        <indexterm><xmlelement>coderef</xmlelement></indexterm>
        <indexterm><xmlelement>codeblock</xmlelement></indexterm>
        <indexterm><xmlatt>format</xmlatt></indexterm>
        <indexterm><xmlatt>outputclass</xmlatt></indexterm>
        <indexterm>encoding</indexterm>
        <indexterm><msgnum>DOTJ052E</msgnum></indexterm>
        <indexterm>character set</indexterm>
      </keywords>
    </metadata>
  </prolog>

  <refbody>
    <section id="coderef-charset">
      <title>Character set definition</title>
      <p>For <xmlelement>coderef</xmlelement> elements, DITA-OT supports defining the code reference target file
        encoding using the <xmlatt>format</xmlatt> attribute. The supported format is:</p>
      <codeblock>format (";" space* "charset=" charset)?</codeblock>
      <p>If a character set is not defined, the system default character set will be used. If the character set is not
        recognized or supported, the <msgnum>DOTJ052E</msgnum> error is thrown and the system default character set is
        used as a fallback.</p>
      <codeblock outputclass="language-xml">&lt;coderef href="unicode.txt" format="txt; charset=UTF-8"/></codeblock>
      <p>As of DITA-OT 3.3, the default character set for code references can be changed by adding the
          <parmname>default.coderef-charset</parmname> key to the
        <xref keyref="configuration-properties-file">configuration.properties</xref> file:</p>
      <codeblock outputclass="language-properties">default.coderef-charset = ISO-8859-1</codeblock>
      <p>The character set values are those supported by the Java
        <xref
          format="html"
          href="https://docs.oracle.com/javase/8/docs/api/java/nio/charset/Charset.html"
          scope="external"
        >Charset</xref> class.</p>
      <note>As of DITA-OT 4.0, the default character set for code references has been changed from the system default
        encoding to UTF-8.</note>
    </section>

    <section>
      <title>Line range extraction</title>
      <p>Code references can be limited to extract only a specified line range by defining the
          <codeph>line-range</codeph> pointer in the URI fragment. The format is:</p>
      <codeblock>uri ("#line-range(" start ("," end)? ")" )?</codeblock>
      <p>Start and end line numbers start from 1 and are inclusive. If the end range is omitted, the range ends on the
        last line of the file.</p>
    </section>
    <example>
      <codeblock
        outputclass="language-xml"
      >&lt;coderef href="Parser.scala#line-range(5,10)" format="scala"/></codeblock>
      <p>Only lines from 5 to 10 will be included in the output.</p>
    </example>
    <section>
      <title>RFC 5147</title>
      <indexterm>RFC 5147</indexterm>
      <p>DITA-OT also supports the line position and range syntax from
        <xref keyref="rfc5147"/>. The format for line range is:</p>
      <codeblock>uri ("#line=" start? "," end? )?</codeblock>
      <p>Start and end line numbers start from 0 and are inclusive and exclusive, respectively. If the start range is
        omitted, the range starts from the first line; if the end range is omitted, the range ends on the last line of
        the file. The format for line position is:</p>
      <codeblock>uri ("#line=" position )?</codeblock>
      <p>The position line number starts from 0.</p>
    </section>
    <example>
      <codeblock outputclass="language-xml">&lt;coderef href="Parser.scala#line=4,10" format="scala"/></codeblock>
      <p>Only lines from 5 to 10 will be included in the output.</p>
    </example>
    <section>
      <title>Line range by content</title>
      <p>Instead of specifying line numbers, you can also select lines to include in the code reference by specifying
        keywords (or “<term>tokens</term>”) that appear in the referenced file.</p>
      <div id="coderef-by-content">
        <p>DITA-OT supports the <codeph>token</codeph> pointer in the URI fragment to extract a line range based on the
          file content. The format for referencing a range of lines by content is:</p>
        <codeblock>uri ("#token=" start? ("," end)? )?</codeblock>
        <p>Lines identified using start and end tokens are exclusive: the lines that contain the start token and end
          token will be not be included. If the start token is omitted, the range starts from the first line in the
          file; if the end token is omitted, the range ends on the last line of the file. </p>
      </div>
    </section>
    <example>
      <p>Given a Haskell source file named <filepath>fact.hs</filepath> with the following content,</p>
      <codeblock outputclass="language-haskell normalize-space show-line-numbers show-whitespace"><coderef
          href="../resources/fact.hs"
        /></codeblock>
      <p>a range of lines can be referenced as:</p>
      <codeblock outputclass="language-xml">&lt;coderef href="fact.hs#token=START-FACT,END-FACT"/></codeblock>
      <p>to include the range of lines that follows the <codeph>START-FACT</codeph> token on Line 1, up to (but not
        including) the line that contains the <codeph>END-FACT</codeph> token (Line 5). The resulting
          <xmlelement>codeblock</xmlelement> would contain lines 2–4:</p>
      <codeblock outputclass="language-haskell"><coderef
          href="../resources/fact.hs#token=START-FACT,END-FACT"
        /></codeblock>
      <note type="tip" id="coderef-by-content-tip">This approach can be used to reference code samples that are
        frequently edited. In these cases, referencing line ranges by line number can be error-prone, as the target line
        range for the reference may shift if preceding lines are added or removed. Specifying ranges by line content
        makes references more robust, as long as the <codeph>token</codeph> keywords are preserved when the referenced
        resource is modified.</note></example>
    <refbodydiv id="normalize-codeblock-whitespace">
      <section>
        <title>Whitespace normalization</title>
        <indexterm>whitespace handling</indexterm>
        <p>DITA-OT can adjust the leading whitespace in code blocks to remove excess indentation and keep lines short.
          Given an XML snippet in a codeblock with lines that all begin with spaces (indicated here as dots “·”),</p>
      </section>
      <example>
        <p><codeblock outputclass="language-xml">··&lt;subjectdef keys="audience">
····&lt;subjectdef keys="novice"/>
····&lt;subjectdef keys="expert"/>
··&lt;/subjectdef></codeblock></p>
        <p>DITA-OT can remove the leading whitespace that is common to all lines in the code block. To trim the excess
          space, set the <xmlatt>outputclass</xmlatt> attribute on the <xmlelement>codeblock</xmlelement> element to
          include the <codeph>normalize-space</codeph> keyword.</p>
        <p>In this case, two spaces (“··”) would be removed from the beginning of each line, shifting content to the
          left by two characters, while preserving the indentation of lines that contain additional whitespace (beyond
          the common indent):</p>
        <p><codeblock outputclass="language-xml">&lt;subjectdef keys="audience">
··&lt;subjectdef keys="novice"/>
··&lt;subjectdef keys="expert"/>
&lt;/subjectdef></codeblock></p>
      </example>
    </refbodydiv>
    <refbodydiv id="visualize-codeblock-whitespace">
      <section>
        <title>Whitespace visualization (PDF)</title>
        <p>DITA-OT can be set to display the whitespace characters in code blocks to visualize indentation in PDF
          output.</p>
        <p>To enable this feature, set the <xmlatt>outputclass</xmlatt> attribute on the
            <xmlelement>codeblock</xmlelement> element to include the <codeph>show-whitespace</codeph> keyword.</p>
        <p>When PDF output is generated, space characters in the code will be replaced with a middle dot or “interpunct”
          character ( <codeph>·</codeph> ); tab characters are replaced with a rightwards arrow and three spaces
            ( <codeph>→   </codeph> ).</p>
      </section>
      <example deliveryTarget="pdf">
        <fig>
          <title>Sample Java code with visible whitespace characters <i>(PDF only)</i></title>
          <codeblock outputclass="language-java show-whitespace">	for i in 0..10 {
		println(i)
	}</codeblock>
        </fig>
      </example>
    </refbodydiv>
    <refbodydiv id="codeblock-line-numbers">
      <section>
        <title>Line numbering (PDF)</title>
        <indexterm>line numbering</indexterm>
        <p>DITA-OT can be set to add line numbers to code blocks to make it easier to distinguish specific lines.</p>
        <p>To enable this feature, set the <xmlatt>outputclass</xmlatt> attribute on the
            <xmlelement>codeblock</xmlelement> element to include the <codeph>show-line-numbers</codeph> keyword.</p>
      </section>
      <example deliveryTarget="pdf">
        <fig>
          <title>Sample Java code with line numbers and visible whitespace characters <i>(PDF only)</i></title>
          <codeblock outputclass="language-java show-line-numbers show-whitespace">	for i in 0..10 {
		println(i)
	}</codeblock>
        </fig>
      </example>
    </refbodydiv>
  </refbody>
</reference>
