<?xml version="1.0" encoding="UTF-8"?>
<chapter id="writing-modes">
    <title>Mode Definition Syntax</title>
    <!-- jEdit buffer-local properties: -->
    <!-- :indentSize=2:noTabs=true: -->
    <!-- :xml.root=users-guide.xml: -->
    <para>Edit modes are defined using XML, the <firstterm>eXtensible Markup
    Language</firstterm>; mode files have the extension
    <filename>.xml</filename>. XML is a very simple language, and as a result
    edit modes are easy to create and modify. This section will start with a
    short XML primer, followed by detailed information about each supported tag
    and highlighting rule.</para>
    <para>Editing a mode or a mode catalog file within jEdit will cause the
    changes to take effect immediately. If you edit modes using another
    application, the changes will take effect after the
    <guimenu>Utilities</guimenu> &gt; <guisubmenu>Troubleshooting</guisubmenu>
    &gt; <guimenuitem>Reload Edit Modes</guimenuitem> command is invoked.</para>
    <section id="xml-primer">
        <title>An XML Primer</title>
        <para>A very simple XML file (which also happens to be an edit mode)
        looks like so:</para>
        <programlisting>&lt;?xml version="1.0"?&gt;

&lt;!DOCTYPE MODE SYSTEM "xmode.dtd"&gt;

&lt;MODE&gt;
    &lt;PROPS&gt;
        &lt;PROPERTY NAME="commentStart" VALUE="/*" /&gt;
        &lt;PROPERTY NAME="commentEnd" VALUE="*/" /&gt;
    &lt;/PROPS&gt;

    &lt;RULES&gt;
        &lt;SPAN TYPE="COMMENT1"&gt;
            &lt;BEGIN&gt;/*&lt;/BEGIN&gt;
            &lt;END&gt;*/&lt;/END&gt;
        &lt;/SPAN&gt;
    &lt;/RULES&gt;
&lt;/MODE&gt;</programlisting>
        <para>Note that each opening tag must have a corresponding closing tag.
        If there is nothing between the opening and closing tags, for example
        <literal>&lt;TAG&gt;&lt;/TAG&gt;</literal>, the shorthand notation
        <literal>&lt;TAG /&gt;</literal> may be used. An example of this
        shorthand can be seen in the <literal>&lt;PROPERTY&gt;</literal> tags
        above.</para>

<tip><title> Validation and Errors </title>

<para> Most XML file formats have a formal grammar specified in either DTD, XSD or RNG.
In the example above, we can see that the <literal>DOCTYPE</literal>,
or formal grammar for jEdit mode files is described in <literal>xmode.dtd</literal>,
which happens to come from jEdit's source code.
If you install the XML plugin, and while editing a mode file in jEdit, go to
<guimenuitem>Plugins - XML - Parse as XML</guimenuitem>,
you should see a structure tree in Sidekick,
and you will also see errors (if there are any) in ErrorList, if the document does not
conform to the proper XML syntax or the document's formal grammar.
In addition, the XML plugin provides completion tips for elements and attributes.
All of these things can help immensely especially when learning XML.
</para>
<para> It is highly recommended that you check your XML files for validation errors
before submitting them to the community. </para></tip>

         <para>XML is case sensitive. <literal>Span</literal> or
        <literal>span</literal> is not the same as
        <literal>SPAN</literal>.</para>
        <para>To insert a special character such as &lt; or &gt; literally in
        XML (for example, inside an attribute value), you must write it as an
        <firstterm>entity</firstterm>. An entity consists of the character's
        symbolic name enclosed within <quote>&amp;</quote> and <quote>;</quote>.
        The most frequently used entities are:</para>
        <itemizedlist>
            <listitem>
                <para><literal>&amp;lt;</literal> - The less-than (&lt;)
                character</para>
            </listitem>
            <listitem>
                <para><literal>&amp;gt;</literal> - The greater-than (&gt;)
                character</para>
            </listitem>
            <listitem>
                <para><literal>&amp;amp;</literal> - The ampersand (&amp;)
                character</para>
            </listitem>
        </itemizedlist>
        <para>For example, the following will cause a syntax error:</para>
        <programlisting>&lt;SEQ TYPE="OPERATOR"&gt;&amp;&lt;/SEQ&gt;</programlisting>
        <para>Instead, you must write:</para>
        <programlisting>&lt;SEQ TYPE="OPERATOR"&gt;&amp;amp;&lt;/SEQ&gt;</programlisting>
        <para>Now that the basics of XML have been covered, the rest of this
        section will cover each construct in detail.</para>
    </section>
    <section id="mode-preamble">
        <title>The Preamble and MODE tag</title>
        <para>Each mode definition must begin with the following:</para>
        <programlisting>&lt;?xml version="1.0"?&gt;
&lt;!DOCTYPE MODE SYSTEM "xmode.dtd"&gt;</programlisting>
        <para>Each mode definition must also contain exactly one
        <literal>MODE</literal> tag. All other tags (<literal>PROPS</literal>,
        <literal>RULES</literal>) must be placed inside the
        <literal>MODE</literal> tag. The <literal>MODE</literal> tag does not
        have any defined attributes. Here is an example:</para>
        <programlisting>&lt;MODE&gt;
    <replaceable>... mode definition goes here ...</replaceable>
&lt;/MODE&gt;</programlisting>
    </section>
    <section id="mode-tag-props">
        <title>The PROPS Tag</title>
        <para>The <literal>PROPS</literal> tag and the
        <literal>PROPERTY</literal> tags inside it are used to define
        mode-specific properties. Each <literal>PROPERTY</literal> tag must have
        a <literal>NAME</literal> attribute set to the property's name, and a
        <literal>VALUE</literal> attribute with the property's value.</para>
        <para>All buffer-local properties listed in <xref
        linkend="buffer-local" /> may be given values in edit modes.</para>

        <para><literal>contextInsensitive</literal> - If true, the property
        indicates that a line can always be highlighted without taking care of
        the previous line. If activated, the syntax parsing will be much faster.
        </para>

        <para>The following mode properties specify commenting strings:</para>
        <itemizedlist>
            <listitem>
                <para><literal>commentEnd</literal> - the comment end string,
                used by the <guimenuitem>Range Comment</guimenuitem>
                command.</para>
            </listitem>
            <listitem>
                <para><literal>commentStart</literal> - the comment start
                string, used by the <guimenuitem>Range Comment</guimenuitem>
                command.</para>
            </listitem>
            <listitem>
                <para><literal>lineComment</literal> - the line comment string,
                used by the <guimenuitem>Line Comment</guimenuitem>
                command.</para>
            </listitem>
        </itemizedlist>
        <para>When performing auto indent, a number of mode properties determine
        the resulting indent level:</para>
        <itemizedlist>
            <listitem>
                <para>The line and the one before it are scanned for brackets
                listed in the <literal>indentCloseBrackets</literal> and
                <literal>indentOpenBrackets</literal> properties. Opening
                brackets in the previous line increase indent.</para>
                <para>If <literal>lineUpClosingBracket</literal> is set to
                <literal>true</literal>, then closing brackets on the current
                line will line up with the line containing the matching opening
                bracket. For example, in Java mode
                <literal>lineUpClosingBracket</literal> is set to
                <literal>true</literal>, resulting in brackets being indented
                like so:</para>
                <programlisting>{
    // Code
    {
        // More code
    }
}</programlisting>
                <para>If <literal>lineUpClosingBracket</literal> is set to
                <literal>false</literal>, the line <emphasis>after</emphasis> a
                closing bracket will be lined up with the line containing the
                matching opening bracket. For example, in Lisp mode
                <literal>lineUpClosingBracket</literal> is set to
                <literal>false</literal>, resulting in brackets being indented
                like so:</para>
                <programlisting>(foo 'a-parameter
    (crazy-p)
    (bar baz ()))
(print "hello world")</programlisting>
            </listitem>
            <listitem>
                <para>If the previous line contains no opening brackets, or if
                the <literal>doubleBracketIndent</literal> property is set to
                <literal>true</literal>, the previous line is checked against
                the regular expressions in the <literal>indentNextLine</literal>
                and <literal>indentNextLines</literal> properties.
                If the
                previous line matches the former, the indent of the current line
                is increased and the subsequent line is shifted back again. If
                the previous line matches the latter, the indent of the current
                and subsequent lines is increased.</para>

                <para> There are corresponding <literal>unindentThisLine</literal> and <literal>unindentNextLines</literal> properties which are checked also, for doing the reverse-indent operation on lines that match certain regular expressions. </para>

                <para>In Java mode, for example, the
                <literal>indentNextLine</literal> property is set to match
                control structures such as <quote>if</quote>,
                <quote>else</quote>, <quote>while</quote>, and so on.</para>
                <para>The <literal>doubleBracketIndent</literal> property, if
                set to the default of <literal>false</literal>, results in code
                indented like so:</para>
                <programlisting>while(objects.hasNext())
{
    Object next = objects.hasNext();
    if(next instanceof Paintable)
        next.paint(g);
}</programlisting>
                <para>On the other hand, settings this property to
                <quote>true</quote> will give the following result:</para>
                <programlisting>while(objects.hasNext())
    {
        Object next = objects.hasNext();
        if(next instanceof Paintable)
            next.paint(g);
    }</programlisting>
            </listitem>
            <listitem><para>
             <literal>electricKeys</literal>: characters listed here, when typed
             on a line, cause the current line to be re-indented. Notice that by
             default, pressing "Enter" does not re-indent the current line, only
             the new line. To get this behavior, add the newline character to
             <literal>electricKeys</literal> in the xml-escaped form &amp;#xA;
             </para></listitem>

             <listitem><para><literal>ignoreWhitespace</literal>:
             Ignore whitespace lines.
             This property is on (<literal>true</literal>) by default.
             Python language sets this to
             <literal>false</literal> because of the special treatment
             of whitespaces. Note this example:
             <programlisting>def fun1:
    a = 1
    b = 2

def fun2:
             </programlisting>
             Pressing <keycap>C+i</keycap>
             (<guimenuitem>Indent Lines</guimenuitem> command) on
             the <literal>fun2</literal> line would usually indent this
             line and make it even with the <literal>b = 2</literal> line.
             But with switched off <literal>ignoreWhitespace</literal> setting
             the line will stay the way it was indented manually.
             <literal>ignoreWhitespace=false</literal> setting prevents
             any forward indentation after a whitespace line.
             </para></listitem>

        </itemizedlist>
        <para>Here is the complete <literal>&lt;PROPS&gt;</literal> tag for Java
        mode:</para>
        <programlisting>&lt;PROPS&gt;
    &lt;PROPERTY NAME="commentStart" VALUE="/*" /&gt;
    &lt;PROPERTY NAME="commentEnd" VALUE="*/" /&gt;
    &lt;PROPERTY NAME="lineComment" VALUE="//" /&gt;
    &lt;PROPERTY NAME="wordBreakChars" VALUE=",+-=&amp;lt;&amp;gt;/?^&amp;amp;*" /&gt;

    &lt;!-- Auto indent --&gt;
    &lt;PROPERTY NAME="indentOpenBrackets" VALUE="{" /&gt;
    &lt;PROPERTY NAME="indentCloseBrackets" VALUE="}" /&gt;
    &lt;PROPERTY NAME="unalignedOpenBrackets" VALUE="(" /&gt;
    &lt;PROPERTY NAME="unalignedCloseBrackets" VALUE=")" /&gt;
    &lt;PROPERTY NAME="indentNextLine"
    	VALUE="\s*(((if|while)\s*\(|else\s*|else\s+if\s*\(|for\s*\(.*\))[^{;]*)" /&gt;
    &lt;PROPERTY NAME="unindentThisLine"
    	VALUE="^.*(default:\s*|case.*:.*)$" /&gt;
    &lt;PROPERTY NAME="electricKeys" VALUE=":" /&gt;
    &lt;!-- set this to 'true' if you want to use GNU coding style --&gt;
    &lt;PROPERTY NAME="doubleBracketIndent" VALUE="false" /&gt;
    &lt;PROPERTY NAME="lineUpClosingBracket" VALUE="true" /&gt;
&lt;/PROPS&gt;</programlisting>
    </section>
    <section id="mode-tag-rules">
        <title>The RULES Tag</title>
        <para><literal>RULES</literal> tags must be placed inside the
        <literal>MODE</literal> tag. Each <literal>RULES</literal> tag defines a
        <firstterm>ruleset</firstterm>. A ruleset consists of a number of
        <firstterm>parser rules</firstterm>, with each parser rule specifying
        how to highlight a specific syntax token. There must be at least one
        ruleset in each edit mode. There can also be more than one, with
        different rulesets being used to highlight different parts of a buffer
        (for example, in HTML mode, one rule set highlights HTML tags, and
        another highlights inline JavaScript). For information about using more
        than one ruleset, see <xref linkend="mode-rule-span" />.</para>
        <para>The <literal>RULES</literal> tag supports the following
        attributes, all of which are optional:</para>
        <itemizedlist>
            <listitem>
                <para><literal>SET</literal> - the name of this ruleset. All
                rulesets other than the first must have a name.</para>
            </listitem>
            <listitem>
                <para><literal>IGNORE_CASE</literal> - if set to
                <literal>FALSE</literal>, matches will be case sensitive.
                Otherwise, case will not matter. Default is
                <literal>TRUE</literal>.</para>
            </listitem>
            <listitem>
                <para><literal>ESCAPE</literal> - specifies a character sequence
                for escaping literals. The first character following the escape
                sequence is not considered as input for syntax highlighting,
                thus being highlighted with default token for the rule set.
                </para>
            </listitem>
            <listitem>
                <para><literal>NO_WORD_SEP</literal> - any non-alphanumeric
                character <emphasis>not</emphasis> in this list is treated as a
                word separator for the purposes of syntax highlighting.</para>
            </listitem>
            <listitem>
                <para><literal>DEFAULT</literal> - the token type for text which
                doesn't match any specific rule. Default is
                <literal>NULL</literal>. See <xref
                linkend="mode-syntax-tokens" /> for a list of token
                types.</para>
            </listitem>
            <listitem>
                <para><literal>HIGHLIGHT_DIGITS</literal></para>
            </listitem>
            <listitem>
                <para><literal>DIGIT_RE</literal> - see below for information
                about these two attributes.</para>
            </listitem>
        </itemizedlist>
        <para>Here is an example <literal>RULES</literal> tag:</para>
        <programlisting>&lt;RULES IGNORE_CASE="FALSE" HIGHLIGHT_DIGITS="TRUE"&gt;
    <replaceable>... parser rules go here ...</replaceable>
&lt;/RULES&gt;</programlisting>
        <section>
            <title>Highlighting Numbers</title>
            <para>If the <literal>HIGHLIGHT_DIGITS</literal> attribute is set to
            <literal>TRUE</literal>, jEdit will attempt to highlight numbers in
            this ruleset.</para>
            <para>Any word consisting entirely of digits (0-9) will be
            highlighted with the <literal>DIGIT</literal> token type. A word
            that contains other letters in addition to digits will be
            highlighted with the <literal>DIGIT</literal> token type only if it
            matches the regular expression specified in the
            <literal>DIGIT_RE</literal> attribute. If this attribute is not
            specified, it will not be highlighted.</para>
            <para>Here is an example <literal>DIGIT_RE</literal> regular
            expression that highlights Java-style numeric literals (normal
            numbers, hexadecimals prefixed with <literal>0x</literal>, numbers
            suffixed with various type indicators, and floating point literals
            containing an exponent). Note that newlines have been inserted here
            for readability.</para>
            <programlisting>DIGIT_RE="(0[lL]?|[1-9]\d{0,9}(\d{0,9}[lL])?
|0[xX]\p{XDigit}{1,8}(\p{XDigit}{0,8}[lL])?
|0[0-7]{1,11}([0-7]{0,11}[lL])?|([0-9]+\.[0-9]*
|\.[0-9]+)([eE][+-]?[0-9]+)?[fFdD]?|[0-9]+([eE][+-]?[0-9]+[fFdD]?
|([eE][+-]?[0-9]+)?[fFdD]))"</programlisting>
            <para>Regular expression syntax is described in <xref
            linkend="regexps" />.</para>
        </section>
        <section id="rule-ordering">
            <title>Rule Ordering Requirements</title>
            <para>You might encounter this very common pitfall when writing your
            own modes.</para>
            <para>Since jEdit checks buffer text against parser rules in the
            order they appear in the ruleset, more specific rules must be placed
            before generalized ones, otherwise the generalized rules will catch
            everything.</para>
            <para>This is best demonstrated with an example. The following is
            incorrect rule ordering:</para>
            <programlisting>&lt;SPAN TYPE="MARKUP"&gt;
    &lt;BEGIN&gt;[&lt;/BEGIN&gt;
    &lt;END&gt;]&lt;/END&gt;
&lt;/SPAN&gt;

&lt;SPAN TYPE="KEYWORD1"&gt;
    &lt;BEGIN&gt;[!&lt;/BEGIN&gt;
    &lt;END&gt;]&lt;/END&gt;
&lt;/SPAN&gt;</programlisting>
            <para>If you write the above in a rule set, any occurrence of
            <quote>[</quote> (even things like <quote>[!DEFINE</quote>, etc)
            will be highlighted using the first rule, because it will be the
            first to match. This is most likely not the intended
            behavior.</para>
            <para>The problem can be solved by placing the more specific rule
            before the general one:</para>
            <programlisting>&lt;SPAN TYPE="KEYWORD1"&gt;
    &lt;BEGIN&gt;[!&lt;/BEGIN&gt;
    &lt;END&gt;]&lt;/END&gt;
&lt;/SPAN&gt;

&lt;SPAN TYPE="MARKUP"&gt;
    &lt;BEGIN&gt;[&lt;/BEGIN&gt;
    &lt;END&gt;]&lt;/END&gt;
&lt;/SPAN&gt;</programlisting>
            <para>Now, if the buffer contains the text
            <quote>[!SPECIAL]</quote>, the rules will be checked in order, and
            the first rule will be the first to match. However, if you write
            <quote>[FOO]</quote>, it will be highlighted using the second rule,
            which is exactly what you would expect.</para>
        </section>
        <section>
            <title>Per-Ruleset Properties</title>
            <para>The <literal>PROPS</literal> tag (described in <xref
            linkend="mode-tag-props" />) can also be placed inside the
            <literal>RULES</literal> tag to define ruleset-specific properties.
            The following properties can be set on a per-ruleset basis:</para>
            <itemizedlist>
                <listitem>
                    <para><literal>commentEnd</literal> - the comment end
                    string.</para>
                </listitem>
                <listitem>
                    <para><literal>commentStart</literal> - the comment start
                    string.</para>
                </listitem>
                <listitem>
                    <para><literal>lineComment</literal> - the line comment
                    string.</para>
                </listitem>
            </itemizedlist>
            <para>This allows different parts of a file to have different
            comment strings (in the case of HTML, for example, in HTML text and
            inline JavaScript). For information about the commenting commands,
            see <xref linkend="commenting" />.</para>
        </section>
    </section>
    <section id="mode-rule-terminate">
        <title>The TERMINATE Tag</title>
        <para>The <literal>TERMINATE</literal> rule, which must be placed inside
        a <literal>RULES</literal> tag, specifies that parsing should stop after
        the specified number of characters have been read from a line. The
        number of characters to terminate after should be specified with the
        <literal>AT_CHAR</literal> attribute. Here is an example:</para>
        <programlisting>&lt;TERMINATE AT_CHAR="1" /&gt;</programlisting>
        <para>This rule is used in Patch mode, for example, because only the
        first character of each line affects highlighting.</para>
    </section>
    <section id="mode-rule-span">
        <title>The SPAN Tag</title>
        <para>The <literal>SPAN</literal> rule, which must be placed inside a
        <literal>RULES</literal> tag, highlights text between a start and end
        string. The start and end strings are specified inside child elements of
        the <literal>SPAN</literal> tag. The following attributes are
        supported:</para>
        <itemizedlist>
            <listitem>
                <para><literal>TYPE</literal> - The token type to highlight the
                span with. See <xref linkend="mode-syntax-tokens" /> for a list
                of token types.</para>
            </listitem>
            <listitem>
                <para><literal>AT_LINE_START</literal> - If set to
                <literal>TRUE</literal>, the span will only be highlighted if
                the start sequence occurs at the beginning of a line.</para>
            </listitem>
            <listitem>
                <para><literal>AT_WHITESPACE_END</literal> - If set to
                <literal>TRUE</literal>, the span will only be highlighted if
                the start sequence is the first non-whitespace text in the
                line.</para>
            </listitem>
            <listitem>
                <para><literal>AT_WORD_START</literal> - If set to
                <literal>TRUE</literal>, the span will only be highlighted if
                the start sequence occurs at the beginning of a word.</para>
            </listitem>
            <listitem>
                <para><literal>DELEGATE</literal> - text inside the span will be
                highlighted with the specified ruleset. To delegate to a ruleset
                defined in the current mode, just specify its name. To delegate
                to a ruleset defined in another mode, specify a name of the form
                <literal><replaceable>mode</replaceable>::<replaceable>ruleset</replaceable></literal>.
                Note that the first (unnamed) ruleset in a mode is called
                <quote>MAIN</quote>.</para>
            </listitem>
            <listitem>
                <para><literal>MATCH_TYPE</literal> - Controls how the start and
                end of the sequence will be highlighted. See <xref
                linkend="mode-match-type" /> for more information.</para>
            </listitem>
            <listitem>
                <para><literal>ESCAPE</literal> - specifies a character sequence
                for escaping characters. The first character following the escape
                sequence is not considered as input for syntax highlighting,
                thus being highlighted with rule's token.
                </para>
            </listitem>
            <listitem>
                <para><literal>NO_LINE_BREAK</literal> - If set to
                <literal>TRUE</literal>, the span will not cross line
                breaks.</para>
            </listitem>
            <listitem>
                <para><literal>NO_WORD_BREAK</literal> - If set to
                <literal>TRUE</literal>, the span will not cross word
                breaks.</para>
            </listitem>
        </itemizedlist>
        <para>Note that the <literal>AT_LINE_START</literal>,
        <literal>AT_WHITESPACE_END</literal> and
        <literal>AT_WORD_START</literal> attributes can also be used on the
        <literal>END</literal> element.</para>
        <para>Here is a <literal>SPAN</literal> that highlights Java string
        literals, which cannot include line breaks:</para>
        <programlisting>&lt;SPAN TYPE="LITERAL1" NO_LINE_BREAK="TRUE"&gt;
  &lt;BEGIN&gt;"&lt;/BEGIN&gt;
  &lt;END&gt;"&lt;/END&gt;
&lt;/SPAN&gt;</programlisting>
        <para>Here is a <literal>SPAN</literal> that highlights Java
        documentation comments by delegating to the <quote>JAVADOC</quote>
        ruleset defined elsewhere in the current mode:</para>
        <programlisting>&lt;SPAN TYPE="COMMENT2" DELEGATE="JAVADOC"&gt;
  &lt;BEGIN&gt;/**&lt;/BEGIN&gt;
  &lt;END&gt;*/&lt;/END&gt;
&lt;/SPAN&gt;</programlisting>
        <para>Here is a <literal>SPAN</literal> that highlights HTML cascading
        stylesheets inside <literal>&lt;STYLE&gt;</literal> tags by delegating
        to the main ruleset in the CSS edit mode:</para>
        <programlisting>&lt;SPAN TYPE="MARKUP" DELEGATE="css::MAIN"&gt;
  &lt;BEGIN&gt;&amp;lt;style&amp;gt;&lt;/BEGIN&gt;
  &lt;END&gt;&amp;lt;/style&amp;gt;&lt;/END&gt;
&lt;/SPAN&gt;</programlisting>
    </section>
    <section id="mode-rule-span-regexp">
        <title>The SPAN_REGEXP Tag</title>
        <para>The <literal>SPAN_REGEXP</literal> rule is similar to the
        <literal>SPAN</literal> rule except the start sequence and optionally
        the end sequence are taken to be regular expressions. In addition to the
        attributes supported by the <literal>SPAN</literal> tag, the following
        attributes are supported:</para>
        <itemizedlist>
            <listitem>
                <para><literal>HASH_CHAR</literal> - a literal string which must
                be at the start of a regular expression.</para>
            </listitem>
            <listitem>
                <para><literal>HASH_CHARS</literal> - a list of possible literal
                characters, one of which must match at the start of the regular
                expression.</para>
            </listitem>
        </itemizedlist>
        <para><literal>HASH_CHAR</literal> and <literal>HASH_CHARS</literal>
        attributes are both optional, but you may only specify one, not both. If
        both are specified, <literal>HASH_CHARS</literal> is ignored and an
        error is shown. Whenever possible, use a literal prefix to specify a
        <literal>SPAN_REGEXP</literal>. If the starting prefix is always the
        same, use <literal>HASH_CHAR</literal> and provide as much prefix as
        possible. Only in rare cases would you omit both attributes, such as the
        case where there is no other reliable way to get the highlighting you
        need, for example, with comments in the Cobol programming
        language.</para>
        <para>In addition, the <literal>END</literal> subtag supports the
        attribute <literal>REGEXP</literal>, which if set to
        <literal>TRUE</literal>, tells the highlighter to interpret the
        <literal>END</literal> text as a regular expression as well.</para>
        <para>The regular expression match cannot span more than one line. Any
        text matched by groups in the <literal>BEGIN</literal> regular
        expression is substituted in the <literal>END</literal> string. See
        below for an example of where this is useful.</para>
        <para>Regular expression syntax is described in <xref
        linkend="regexps" />.</para>
        <para>Here is a <literal>SPAN_REGEXP</literal> rule that highlights
        <quote>read-ins</quote> in shell scripts:</para>
        <programlisting>&lt;SPAN_REGEXP HASH_CHAR="&amp;lt;" TYPE="LITERAL1" DELEGATE="LITERAL"&gt;
    &lt;BEGIN&gt;&lt;![CDATA[&lt;&lt;[\p{Space}'"]*([\p{Alnum}_]+)[\p{Space}'"]*]]&gt;&lt;/BEGIN&gt;
    &lt;END&gt;$1&lt;/END&gt;
&lt;/SPAN_REGEXP&gt;</programlisting>
        <para>Here is a <literal>SPAN_REGEXP</literal> rule that highlights
        constructs placed between <literal>&lt;#ftl</literal> and
        <literal>&gt;</literal>, as long as the <literal>&lt;#ftl</literal> is
        followed by a word break:</para>
        <programlisting>&lt;SPAN_REGEXP TYPE="KEYWORD1" HASH_CHAR="&amp;lt;" DELEGATE="EXPRESSION"&gt;
    &lt;BEGIN&gt;&amp;lt;#ftl\b&lt;/BEGIN&gt;
    &lt;END&gt;&amp;gt;&lt;/END&gt;
&lt;/SPAN_REGEXP&gt;</programlisting>
    </section>
    <section id="mode-rule-eol-span">
        <title>The EOL_SPAN Tag</title>
        <para>An <literal>EOL_SPAN</literal> is similar to a
        <literal>SPAN</literal> except that highlighting stops at the end of the
        line, and no end sequence needs to be specified. The text to match is
        specified between the opening and closing <literal>EOL_SPAN</literal>
        tags. The following attributes are supported:</para>
        <itemizedlist>
            <listitem>
                <para><literal>TYPE</literal> - The token type to highlight the
                span with. See <xref linkend="mode-syntax-tokens" /> for a list
                of token types.</para>
            </listitem>
            <listitem>
                <para><literal>AT_LINE_START</literal> - If set to
                <literal>TRUE</literal>, the span will only be highlighted if
                the start sequence occurs at the beginning of a line.</para>
            </listitem>
            <listitem>
                <para><literal>AT_WHITESPACE_END</literal> - If set to
                <literal>TRUE</literal>, the span will only be highlighted if
                the sequence is the first non-whitespace text in the
                line.</para>
            </listitem>
            <listitem>
                <para><literal>AT_WORD_START</literal> - If set to
                <literal>TRUE</literal>, the span will only be highlighted if
                the start sequence occurs at the beginning of a word.</para>
            </listitem>
            <listitem>
                <para><literal>DELEGATE</literal> - text inside the span will be
                highlighted with the specified ruleset. To delegate to a ruleset
                defined in the current mode, just specify its name. To delegate
                to a ruleset defined in another mode, specify a name of the form
                <literal><replaceable>mode</replaceable>::<replaceable>ruleset</replaceable></literal>.
                Note that the first (unnamed) ruleset in a mode is called
                <quote>MAIN</quote>.</para>
            </listitem>
            <listitem>
                <para><literal>MATCH_TYPE</literal> - Controls how the start of
                the sequence will be highlighted. See <xref
                linkend="mode-match-type" /> for more information.</para>
            </listitem>
        </itemizedlist>
        <para>Here is an <literal>EOL_SPAN</literal> that highlights C++
        comments:</para>
        <programlisting>&lt;EOL_SPAN TYPE="COMMENT1"&gt;//&lt;/EOL_SPAN&gt;</programlisting>
    </section>
    <section id="mode-rule-eol-span-regexp">
        <title>The EOL_SPAN_REGEXP Tag</title>
        <para>The <literal>EOL_SPAN_REGEXP</literal> rule is similar to the
        <literal>EOL_SPAN</literal> rule except the match sequence is taken to
        be a regular expression. In addition to the attributes supported by the
        <literal>EOL_SPAN</literal> tag, the following attributes are
        supported:</para>
        <itemizedlist>
            <listitem>
                <para><literal>HASH_CHAR</literal> - a literal string which must
                be at the start of a regular expression.</para>
            </listitem>
            <listitem>
                <para><literal>HASH_CHARS</literal> - a list of possible literal
                characters, one of which must match at the start of the regular
                expression.</para>
            </listitem>
        </itemizedlist>
        <para><literal>HASH_CHAR</literal> and <literal>HASH_CHARS</literal>
        attributes are both optional, but you may only specify one, not both. If
        both are specified, <literal>HASH_CHARS</literal> is ignored and an
        error is shown. Whenever possible, use a literal prefix to specify a
        <literal>EOL_SPAN_REGEXP</literal>. If the starting prefix is always the
        same, use <literal>HASH_CHAR</literal> and provide as much prefix as
        possible. Only in rare cases would you omit both attributes, such as the
        case where there is no other reliable way to get the highlighting you
        need, for example, with comments in the Cobol programming
        language.</para>
        <para>The regular expression match cannot span more than one
        line.</para>
        <para>Regular expression syntax is described in <xref
        linkend="regexps" />.</para>
        <para>Here is an <literal>EOL_SPAN_REGEXP</literal> that highlights
        MS-DOS batch file comments, which start with <literal>REM</literal>,
        followed by any whitespace character, and extend until the end of the
        line:</para>
        <programlisting>&lt;EOL_SPAN_REGEXP AT_WHITESPACE_END="TRUE" HASH_CHAR="REM" TYPE="COMMENT1"&gt;REM\s&lt;/EOL_SPAN_REGEXP&gt;</programlisting>
    </section>
    <section id="mode-rule-mark-prev">
        <title>The MARK_PREVIOUS Tag</title>
        <para>The <literal>MARK_PREVIOUS</literal> rule, which must be placed
        inside a <literal>RULES</literal> tag, highlights from the end of the
        previous syntax token to the matched text. The text to match is
        specified between opening and closing <literal>MARK_PREVIOUS</literal>
        tags. The following attributes are supported:</para>
        <itemizedlist>
            <listitem>
                <para><literal>TYPE</literal> - The token type to highlight the
                text with. See <xref linkend="mode-syntax-tokens" /> for a list
                of token types.</para>
            </listitem>
            <listitem>
                <para><literal>AT_LINE_START</literal> - If set to
                <literal>TRUE</literal>, the sequence will only be highlighted
                if it occurs at the beginning of a line.</para>
            </listitem>
            <listitem>
                <para><literal>AT_WHITESPACE_END</literal> - If set to
                <literal>TRUE</literal>, the sequence will only be highlighted
                if it is the first non-whitespace text in the line.</para>
            </listitem>
            <listitem>
                <para><literal>AT_WORD_START</literal> - If set to
                <literal>TRUE</literal>, the sequence will only be highlighted
                if it occurs at the beginning of a word.</para>
            </listitem>
            <listitem>
                <para><literal>MATCH_TYPE</literal> - Controls how the matched
                region will be highlighted. See <xref
                linkend="mode-match-type" /> for more information.</para>
            </listitem>
        </itemizedlist>
        <para>Here is a rule that highlights labels in Java mode (for example,
        <quote>XXX:</quote>):</para>
        <programlisting>&lt;MARK_PREVIOUS AT_WHITESPACE_END="TRUE"
   MATCH_TYPE="DEFAULT"&gt;:&lt;/MARK_PREVIOUS&gt;</programlisting>
    </section>
    <section id="mode-rule-mark-following">
        <title>The MARK_FOLLOWING Tag</title>
        <para>The <literal>MARK_FOLLOWING</literal> rule, which must be placed
        inside a <literal>RULES</literal> tag, highlights from the start of the
        match to the next syntax token. The text to match is specified between
        opening and closing <literal>MARK_FOLLOWING</literal> tags. The
        following attributes are supported:</para>
        <itemizedlist>
            <listitem>
                <para><literal>TYPE</literal> - The token type to highlight the
                text with. See <xref linkend="mode-syntax-tokens" /> for a list
                of token types.</para>
            </listitem>
            <listitem>
                <para><literal>AT_LINE_START</literal> - If set to
                <literal>TRUE</literal>, the sequence will only be highlighted
                if it occurs at the beginning of a line.</para>
            </listitem>
            <listitem>
                <para><literal>AT_WHITESPACE_END</literal> - If set to
                <literal>TRUE</literal>, the sequence will only be highlighted
                if it is the first non-whitespace text in the line.</para>
            </listitem>
            <listitem>
                <para><literal>AT_WORD_START</literal> - If set to
                <literal>TRUE</literal>, the sequence will only be highlighted
                if it occurs at the beginning of a word.</para>
            </listitem>
            <listitem>
                <para><literal>MATCH_TYPE</literal> - Controls how the matched
                region will be highlighted. See <xref
                linkend="mode-match-type" /> for more information.</para>
            </listitem>
        </itemizedlist>
        <para>Here is a rule that highlights variables in Unix shell scripts
        (<quote>$CLASSPATH</quote>, <quote>$IFS</quote>, etc):</para>
        <programlisting>&lt;MARK_FOLLOWING TYPE="KEYWORD2"&gt;$&lt;/MARK_FOLLOWING&gt;</programlisting>
    </section>
    <section id="mode-rule-seq">
        <title>The SEQ Tag</title>
        <para>The <literal>SEQ</literal> rule, which must be placed inside a
        <literal>RULES</literal> tag, highlights fixed sequences of text. The
        text to highlight is specified between opening and closing
        <literal>SEQ</literal> tags. The following attributes are
        supported:</para>
        <itemizedlist>
            <listitem>
                <para><literal>TYPE</literal> - the token type to highlight the
                sequence with. See <xref linkend="mode-syntax-tokens" /> for a
                list of token types.</para>
            </listitem>
            <listitem>
                <para><literal>AT_LINE_START</literal> - If set to
                <literal>TRUE</literal>, the sequence will only be highlighted
                if it occurs at the beginning of a line.</para>
            </listitem>
            <listitem>
                <para><literal>AT_WHITESPACE_END</literal> - If set to
                <literal>TRUE</literal>, the sequence will only be highlighted
                if it is the first non-whitespace text in the line.</para>
            </listitem>
            <listitem>
                <para><literal>AT_WORD_START</literal> - If set to
                <literal>TRUE</literal>, the sequence will only be highlighted
                if it occurs at the beginning of a word.</para>
            </listitem>
            <listitem>
                <para><literal>DELEGATE</literal> - if this attribute is
                specified, all text after the sequence will be highlighted using
                this ruleset. To delegate to a ruleset defined in the current
                mode, just specify its name. To delegate to a ruleset defined in
                another mode, specify a name of the form
                <literal><replaceable>mode</replaceable>::<replaceable>ruleset</replaceable></literal>.
                Note that the first (unnamed) ruleset in a mode is called
                <quote>MAIN</quote>.</para>
            </listitem>
        </itemizedlist>
        <para>The following rules highlight a few Java operators:</para>
        <programlisting>&lt;SEQ TYPE="OPERATOR"&gt;+&lt;/SEQ&gt;
&lt;SEQ TYPE="OPERATOR"&gt;-&lt;/SEQ&gt;
&lt;SEQ TYPE="OPERATOR"&gt;*&lt;/SEQ&gt;
&lt;SEQ TYPE="OPERATOR"&gt;/&lt;/SEQ&gt;</programlisting>
    </section>
    <section id="mode-rule-seq-regexp">
        <title>The SEQ_REGEXP Tag</title>
        <para>The <literal>SEQ_REGEXP</literal> rule is similar to the
        <literal>SEQ</literal> rule except the match sequence is taken to be a
        regular expression. In addition to the attributes supported by the
        <literal>SEQ</literal> tag, the following attributes are
        supported:</para>
        <itemizedlist>
            <listitem>
                <para><literal>HASH_CHAR</literal> - a literal string which must
                be at the start of a regular expression.</para>
            </listitem>
            <listitem>
                <para><literal>HASH_CHARS</literal> - a list of possible literal
                characters, one of which must match at the start of the regular
                expression.</para>
            </listitem>
        </itemizedlist>
        <para><literal>HASH_CHAR</literal> and <literal>HASH_CHARS</literal>
        attributes are both optional, but you may only specify one, not both. If
        both are specified, <literal>HASH_CHARS</literal> is ignored and an
        error is shown. Whenever possible, use a literal prefix to specify a
        <literal>SEQ_REGEXP</literal>. If the starting prefix is always the
        same, use <literal>HASH_CHAR</literal> and provide as much prefix as
        possible. Only in rare cases would you omit both attributes, such as the
        case where there is no other reliable way to get the highlighting you
        need, for example, with comments in the Cobol programming
        language.</para>
        <para>The regular expression match cannot span more than one
        line.</para>
        <para>Regular expression syntax is described in <xref
        linkend="regexps" />.</para>
        <para><emphasis role="bold">NOTE</emphasis>: c-style character escaping
        for literals (such as the tab char: \t) do not work as attribute values
        in XML. Use the XML character entity instead. For example: &amp;#09;
        instead of \t.</para>
        <para>Here is a <literal>SEQ_REGEXP</literal> rule from moin.xml that
        uses the <literal>HASH_CHARS</literal> attribute, to describe a keyword
        (wikiword) that can start with any uppercase letter and contain lower
        case letters and at least one uppercase letter in the middle.</para>
        <programlisting>
 		&lt;SEQ_REGEXP HASH_CHARS="ABCDEFGHIJKLMNOPQRSTUVWXYZ" AT_WORD_START="TRUE"
 		TYPE="KEYWORD2"&gt;[A-Z][a-z]+[A-Z][a-zA-Z]+&lt;/SEQ_REGEXP&gt;
 </programlisting>
    </section>
    <section id="mode-rule-import">
        <title>The IMPORT Tag</title>
        <para>The <literal>IMPORT</literal> tag, which must be placed inside a
        <literal>RULES</literal> tag, loads all rules defined in a given ruleset
        into the current ruleset; in other words, it has the same effect as
        copying and pasting the imported ruleset.</para>
        <para>The only required attribute <literal>DELEGATE</literal> must be
        set to the name of a ruleset. To import a ruleset defined in the current
        mode, just specify its name. To import a ruleset defined in another
        mode, specify a name of the form
        <literal><replaceable>mode</replaceable>::<replaceable>ruleset</replaceable></literal>.
        Note that the first (unnamed) ruleset in a mode is called
        <quote>MAIN</quote>.</para>
        <para>One quirk is that the definition of the imported ruleset is not
        copied to the location of the <literal>IMPORT</literal> tag, but rather
        to the end of the containing ruleset. This has implications with
        rule-ordering; see <xref linkend="rule-ordering" />.</para>
        <para>Here is an example from the PHP mode, which extends the inline
        JavaScript highlighting to support embedded PHP:</para>
        <programlisting>
   &lt;RULES SET="JAVASCRIPT+PHP"&gt;

   &lt;SPAN TYPE="MARKUP" DELEGATE="php::PHP"&gt;
       &lt;BEGIN&gt;&amp;lt;?php&lt;/BEGIN&gt;
       &lt;END&gt;?&amp;gt;&lt;/END&gt;
   &lt;/SPAN&gt;

   &lt;SPAN TYPE="MARKUP" DELEGATE="php::PHP"&gt;
       &lt;BEGIN&gt;&amp;lt;?&lt;/BEGIN&gt;
       &lt;END&gt;?&amp;gt;&lt;/END&gt;
   &lt;/SPAN&gt;

   &lt;SPAN TYPE="MARKUP" DELEGATE="php::PHP"&gt;
       &lt;BEGIN&gt;&amp;lt;%=&lt;/BEGIN&gt;
       &lt;END&gt;%&amp;gt;&lt;/END&gt;
   &lt;/SPAN&gt;

   &lt;IMPORT DELEGATE="javascript::MAIN"/&gt;
&lt;/RULES&gt;</programlisting>
    </section>
    <section id="mode-rule-keywords">
        <title>The KEYWORDS Tag</title>
        <para>The <literal>KEYWORDS</literal> tag, which must be placed inside a
        <literal>RULES</literal> tag and can only appear once, specifies a list
        of keywords to highlight. Keywords are similar to
        <literal>SEQ</literal>s, except that <literal>SEQ</literal>s match
        anywhere in the text, whereas keywords only match whole words. Words are
        considered to be runs of text separated by non-alphanumeric
        characters.</para>
        <para>The <literal>KEYWORDS</literal> tag does not define any
        attributes.</para>
        <para>Each child element of the <literal>KEYWORDS</literal> tag is an
        element whose name is a token type, and whose content is the keyword to
        highlight. For example, the following rule highlights the most common
        Java keywords:</para>
        <programlisting>&lt;KEYWORDS&gt;
  &lt;KEYWORD1&gt;if&lt;/KEYWORD1&gt;
  &lt;KEYWORD1&gt;else&lt;/KEYWORD1&gt;
  &lt;KEYWORD3&gt;int&lt;/KEYWORD3&gt;
  &lt;KEYWORD3&gt;void&lt;/KEYWORD3&gt;
&lt;/KEYWORDS&gt;</programlisting>
    </section>
    <section id="mode-syntax-tokens">
        <title>Token Types</title>
        <para>The various token types are used to syntax highlight particular
        words in a language. This makes code easier to read. There is a wide
        latitude in the usage of the token types, and really it depends on the
        specifics of the language as to which token represents which type. Some
        examples are given below, but these are just guidelines, not hard and
        fast rules.</para>
        <para>Many languages include constructs from other languages. One common
        example is html files can include javascript and css blocks. Several of
        the mode tags support a DELEGATE attribute, which will allow a section
        of text to be passed to a different mode for highlighting. The html mode
        delegates to the javascript mode for javascript blocks and to the css
        mode for style blocks. Use of the DELEGATE attribute is highly encouraged
        when appropriate since it makes writing modes easier, reduces duplication,
        and promotes visual consistency across languages.</para>
        <para>Parser rules can highlight tokens using any of the following token
        types:</para>
        <itemizedlist>
            <listitem>
                <para><literal>NULL</literal> - no special highlighting is
                performed on tokens of type <literal>NULL</literal></para>
            </listitem>
            <listitem>
                <para><literal>COMMENT1</literal></para>
            </listitem>
            <listitem>
                <para><literal>COMMENT2</literal></para>
            </listitem>
            <listitem>
                <para><literal>COMMENT3</literal></para>
            </listitem>
            <listitem>
                <para><literal>COMMENT4</literal></para>
                <para>jEdit supports four different types of comment tokens.
                Generally, comments are programmer-readable constructs that are
                ignored by compilers and interpreters. As an example, the lisp
                mode defines four comment types:
                </para>
                <para>&lt;EOL_SPAN TYPE="COMMENT4"&gt;;;;;&lt;/EOL_SPAN&gt;</para>
                <para>&lt;EOL_SPAN TYPE="COMMENT3"&gt;;;;&lt;/EOL_SPAN&gt;</para>
                <para>&lt;EOL_SPAN TYPE="COMMENT2"&gt;;;&lt;/EOL_SPAN&gt;</para>
                <para>&lt;EOL_SPAN TYPE="COMMENT1"&gt;;&lt;/EOL_SPAN&gt;</para>
            </listitem>
            <listitem>
                <para><literal>FUNCTION</literal></para>
                <para>The function token is intended to identify functions, methods,
                procedures, routines, or named subprograms.</para>
            </listitem>
            <listitem>
               <para><literal>DIGIT</literal></para>
               <para>The digit token is to identify numbers.</para>
            </listitem>
            <listitem>
                <para><literal>INVALID</literal><!--  - tokens of this type are
  automatically added if a <literal>NO_WORD_BREAK</literal> or
  <literal>NO_LINE_BREAK</literal> <literal>SPAN</literal> spans more than
  one word or line, respectively. --></para>
                <para>The invalid type is to indicate that particular words are
                not to be used, for example, the java mode defined both "goto"
                and "const" as invalid words. These are words that are defined
                by the language, but are not to be used.</para>
            </listitem>
            <listitem>
                <para><literal>KEYWORD1</literal></para>
            </listitem>
            <listitem>
                <para><literal>KEYWORD2</literal></para>
            </listitem>
            <listitem>
                <para><literal>KEYWORD3</literal></para>
            </listitem>
            <listitem>
                <para><literal>KEYWORD4</literal></para>
                <para>
                    Keywords are used to identify well-defined words within a
                    language. Some languages naturally divide keywords into
                    groups, for example, the pascal mode identifies "for" as a
                    KEYWORD1, "private" as a KEYWORD2, and "int" as a KEYWORD3.
                </para>
            </listitem>
            <listitem>
                <para><literal>LABEL</literal></para>
                <para>A label is generally a named position within a source, for
                example, the ada mode defined a label as &lt;&lt;foo&gt;&gt;.
                </para>
            </listitem>
            <listitem>
                <para><literal>LITERAL1</literal></para>
            </listitem>
            <listitem>
                <para><literal>LITERAL2</literal></para>
            </listitem>
            <listitem>
                <para><literal>LITERAL3</literal></para>
            </listitem>
            <listitem>
                <para><literal>LITERAL4</literal></para>
                <para>
                    Literals are usually, but not always, uninterpreted strings,
                    for example, "foo" or 'bar'. There are a wide variety of
                    usages of literals in the mode files.
                </para>
            </listitem>
            <listitem>
                <para><literal>MARKUP</literal></para>
                <para>
                    The markup token is generally used in the various "markup"
                    languages, such as xml and html. Markup is used for those
                    elements that are not specified as words belonging to the
                    language. For example, in html, &lt;body&gt; would be
                    considered a keyword, where &lt;foo&gt; would be considered
                    markup.
                </para>
            </listitem>
            <listitem>
                <para><literal>OPERATOR</literal></para>
                <para>
                    Common examples of operators are the math symbols, such as
                    '+', '-', and so on.
                </para>
            </listitem>
        </itemizedlist>
    </section>
    <section id="mode-match-type">
        <title>The MATCH_TYPE Attribute</title>
        <para>The <literal>MATCH_TYPE</literal> attribute is used by some of the
        rules to control how the region matched by the rule will be
        highlighted.</para>
        <para>For example, when using a <literal>MARK_PREVIOUS</literal> rule to
        highlight a function call of the form <literal>fcall()</literal>, the
        following rule could be used:</para>
        <programlisting>
   &lt;MARK_PREVIOUS TYPE="FUNCTION" MATCH_TYPE="OPERATOR"&gt;(&lt;/MARK_PREVIOUS&gt;</programlisting>
        <para>This would cause <literal>fcall</literal> to be highlighted as
        <literal>FUNCTION</literal>, and <literal>(</literal> to be highlighted
        as <literal>OPERATOR</literal>. In this case, to maintain bracket
        matching working, a <literal>SEQ</literal> rule would have to be added
        to match <literal>)</literal> and mark it as
        <literal>OPERATOR</literal>.</para>
        <para>The <literal>MATCH_TYPE</literal> attribute value can be any of
        the valid token types, or the following special values:</para>
        <itemizedlist>
            <listitem>
                <para><literal>RULE</literal>: this is the default value. It
                tells the syntax system to use the same token type as the TYPE
                attribute of the rule. This is equivalent to
                <literal>EXCLUDE_MATCH="FALSE"</literal> in 4.2 and earlier mode
                files.</para>
            </listitem>
            <listitem>
                <para><literal>CONTEXT</literal>: using this value tells the
                syntax system to mark the matched region using the default token
                type for the current rule set. In 4.2 and earlier mode files,
                this was specified by
                <literal>EXCLUDE_MATCH="TRUE"</literal>.</para>
            </listitem>
        </itemizedlist>
    </section>
</chapter>
