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authorTimothy Pearson <kb9vqf@pearsoncomputing.net>2011-12-03 11:05:10 -0600
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+<appendix id="highlight">
+<title>Working with Syntax Higlighting</title>
+
+<sect1 id="highlight-overview">
+
+<title>Overview</title>
+
+<para>Syntax Highlighting is what makes the editor automatically
+display text in different styles/colors, depending on the function of
+the string in relation to the purpose of the file. In program source
+code for example, control statements may be rendered bold, while data
+types and comments get different colors from the rest of the
+text. This greatly enhances the readability of the text, and thus
+helps the author to be more efficient and productive.</para>
+
+<mediaobject>
+<imageobject><imagedata format="PNG" fileref="highlighted.png"/></imageobject>
+<textobject><phrase>A perl function, rendered with syntax
+highlighting.</phrase></textobject>
+<caption><para>A perl function, rendered with syntax highlighting.</para>
+</caption>
+</mediaobject>
+
+<mediaobject>
+<imageobject><imagedata format="PNG" fileref="unhighlighted.png"/></imageobject>
+<textobject><phrase>The same perl function, without
+highlighting.</phrase></textobject>
+<caption><para>The same perl function, without highlighting.</para></caption>
+</mediaobject>
+
+<para>Of the two examples, which is easiest to read?</para>
+
+<para>&kate; comes with a flexible, configurable and capable system
+for doing syntax highlighting, and the standard distribution provides
+definitions for a wide range of programming languages, markup and
+scripting languages and other text file formats. In addition you can
+provide your own definitions in simple &XML; files.</para>
+
+<para>&kate; will automatically detect the right syntax rules when you
+open a file, based on the &MIME; Type of the file, determined by its
+extension, or, if it has none, the contents. Should you experience a
+bad choice, you can manually set the syntax to use from the
+<menuchoice><guimenu>Documents</guimenu><guisubmenu>Highlight
+Mode</guisubmenu></menuchoice> menu.</para>
+
+<para>The styles and colors used by each syntax highlight definition,
+as well as which &MIME;types it should be used for, can be configured
+using the <link linkend="config-dialog-editor-hl"> Highlight</link>
+page of the <link linkend="config-dialog">Config Dialog</link>.</para>
+
+<note>
+<para>Syntax highlighting is there to enhance the readability of
+correct text, but you cannot trust it to validate your text. Marking
+text for syntax is difficult depending on the format you are using,
+and in some cases the authors of the syntax rules will be proud if 98%
+of text gets correctly rendered, though most often you need a rare
+style to see the incorrect 2%.</para>
+</note>
+
+<tip>
+<para>You can download updated or additional syntax highlight
+definitions from the &kate; website by clicking the
+<guibutton>Download</guibutton> button in the <link
+linkend="config-dialog-editor-hl">Highlight Page</link> of the <link
+linkend="config-dialog">Config Dialog</link>.</para>
+</tip>
+
+</sect1>
+
+<sect1 id="katehighlight-system">
+
+<title>The &kate; Syntax Highlight System</title>
+
+<para>This section will discuss the &kate; syntax highlighting
+mechanism in more detail. It is for you if you want to know know about
+it, or if you want to change or create syntax definitions.</para>
+
+<sect2 id="katehighlight-howitworks">
+
+<title>How it Works</title>
+
+<para>Whenever you open a file, one of the first things the &kate;
+editor does is detect which syntax definition to use for the
+file. While reading the text of the file, and while you type away in
+it, the syntax highlighting system will analyze the text using the
+rules defined by the syntax definition and mark in it where different
+contexts and styles begin and end.</para>
+
+<para>When you type in the document, the new text is analyzed and marked on the
+fly, so that if you delete a character that is marked as the beginning or end
+of a context, the style of surrounding text changes accordingly.</para>
+
+<para>The syntax definitions used by the &kate; syntax highlighting system are
+&XML; files, containing
+<itemizedlist>
+<listitem><para>Rules for detecting the role of text, organized into context blocks</para></listitem>
+<listitem><para>Keyword lists</para></listitem>
+<listitem><para>Style Item definitions</para></listitem>
+</itemizedlist>
+</para>
+
+<para>When analyzing the text, the detection rules are evaluated in
+the order in which they are defined, and if the beginning of the
+current string matches a rule, the related context is used. The start
+point in the text is moved to the final point at which that rule
+matched and a new loop of the rules begins, starting in the context
+set by the matched rule.</para>
+
+</sect2>
+
+<sect2 id="highlight-system-rules">
+<title>Rules</title>
+
+<para>The detection rules are the heart of the highlighting detection
+system. A rule is a string, character or <link
+linkend="regular-expressions">regular expression</link> against which
+to match the text being analyzed. It contains information about which
+style to use for the matching part of the text. It may switch the
+working context of the system either to an explicitly mentioned
+context or to the previous context used by the text.</para>
+
+<para>Rules are organized in context groups. A context group is used
+for main text concepts within the format, for example quoted text
+strings or comment blocks in program source code. This ensures that
+the highlighting system does not need to loop through all rules when
+it is not necessary, and that some character sequences in the text can
+be treated differently depending on the current context.
+</para>
+
+</sect2>
+
+<sect2 id="highlight-context-styles-keywords">
+<title>Context Styles and Keywords</title>
+
+<para>In some programming languages, integer numbers are treated
+differently than floating point ones by the compiler (the program that
+converts the source code to a binary executable), and there may be
+characters having a special meaning within a quoted string. In such
+cases, it makes sense to render them differently from the surroundings
+so that they are easy to identify while reading the text. So even if
+they do not represent special contexts, they may be seen as such by
+the syntax highlighting system, so that they can be marked for
+different rendering.</para>
+
+<para>A syntax definition may contain as many styles as required to
+cover the concepts of the format it is used for.</para>
+
+<para>In many formats, there are lists of words that represent a
+specific concept. For example in programming languages, the control
+statements is one concept, data type names another, and built in
+functions of the language a third. The &kate; Syntax Highlighting
+System can use such lists to detect and mark words in the text to
+emphasize concepts of the text formats.</para>
+
+</sect2>
+
+<sect2 id="kate-highlight-system-default-styles">
+<title>Default Styles</title>
+
+<para>If you open a C++ source file, a &Java; source file and an
+<acronym>HTML</acronym> document in &kate;, you will see that even
+though the formats are different, and thus different words are chosen
+for special treatment, the colors used are the same. This is because
+&kate; has a predefined list of Default Styles, that are employed by
+the individual syntax definitions.</para>
+
+<para>This makes it easy to recognize similar concepts in different
+text formats. For example comments are present in almost any
+programming, scripting or markup language, and when they are rendered
+using the same style in all languages, you do not have to stop and
+think to identify them within the text.</para>
+
+<tip>
+<para>All styles in a syntax definition use one of the default
+styles. A few syntax definitions use more styles that there are
+defaults, so if you use a format often, it may be worth launching the
+configuration dialog to see if some concepts are using the same
+style. For example there is only one default style for strings, but as
+the perl programming language operates with two types of strings, you
+can enhance the highlighting by configuring those to be slightly
+different.</para>
+</tip>
+
+</sect2>
+
+</sect1>
+
+<sect1 id="katehighlight-xml-format">
+<title>The Highlight Definition &XML; Format</title>
+
+<sect2>
+<title>Overview</title>
+
+<para>This section is an overview of the Highlight Definition &XML;
+format. It will describe the main components and their meaning and
+usage, and go into detail with the detection rules.</para>
+
+<para>The formal definition, aka the <acronym>DTD</acronym> is stored
+in the file <filename>language.dtd</filename> which should be
+installed on your system in the directory
+<filename>$<envar>KDEDIR</envar>/share/apps/kate/syntax</filename>.</para>
+
+<variablelist>
+<title>Main components of &kate; Highlight Definitions</title>
+
+<varlistentry>
+<term>The General Section</term>
+<listitem>
+<para>The General Section contains information on the comment format
+of the described language, and defines whether keywords are case
+sensitive.</para>
+</listitem>
+</varlistentry>
+
+<varlistentry>
+<term>Highlighting</term>
+<listitem>
+<para>The Highlighting section contains all data required to analyze
+and render the text. This includes:</para>
+
+<variablelist>
+<varlistentry>
+<term>ItemDatas</term>
+<listitem><para>Contains ItemData elements, each defining a
+style.</para></listitem>
+</varlistentry>
+
+<varlistentry>
+<term>Keyword lists</term>
+<listitem>
+<para>Each list has a name, and may contain any number of items.</para>
+</listitem>
+</varlistentry>
+
+<varlistentry>
+<term>Contexts</term>
+<listitem>
+<para>Contains contexts, which again contain the syntax detection rules.</para>
+</listitem>
+</varlistentry>
+</variablelist>
+
+</listitem>
+</varlistentry>
+
+</variablelist>
+
+</sect2>
+
+</sect1>
+
+<sect1 id="kate-highlight-rules-detailled">
+<title>Highlight Detection Rules</title>
+
+<para>This section describes the syntax detection rules.</para>
+
+<para>Each rule can match zero or more characters at the beginning of
+the string they are asked to test. If the rule matches, the matching
+characters are assigned the style or <emphasis>attribute</emphasis>
+defined by the rule, and a rule may ask that the current context is
+switched.</para>
+
+<para>The <emphasis>attribute</emphasis> and
+<emphasis>context</emphasis> attributes are common to all
+rules.</para>
+
+<para>A rule looks like this:</para>
+
+<programlisting>&lt;RuleName attribute=&quot;(identifier)&quot; context=&quot;(identifier|order)&quot; [rule specific attributes] /&gt;</programlisting>
+
+<para>The <emphasis>attribute</emphasis> identifies the style to use
+for matched characters by name or index, and the
+<emphasis>context</emphasis> identifies the context to use from
+here.</para>
+
+<para>The <emphasis>attribute</emphasis> can be identified either by
+name, or by its zero-based index in the ItemDatas group.</para>
+
+<para>The <emphasis>context</emphasis> can be identified by:</para>
+
+<itemizedlist>
+<listitem>
+<para>An <emphasis>identifier</emphasis>, currently only its zero-based
+index in the contexts group.</para>
+</listitem>
+<listitem>
+<para>An <emphasis>order</emphasis> telling the engine to stay in the
+current context (<userinput>#stay</userinput>), or to pop back to a
+previous context used in the string
+(<userinput>#pop</userinput>).</para>
+<para>To go back more steps, the #pop keyword can be repeated:
+<userinput>#pop#pop#pop</userinput></para>
+</listitem>
+</itemizedlist>
+
+<para>Some rules can have <emphasis>child rules</emphasis> which are
+then evaluated if and only if the parent rule matched. The entire
+matched string will be given the attribute defined by the parent
+rule. A rule with child rules looks like this:</para>
+
+<programlisting>
+&lt;RuleName (attributes)&gt;
+ &lt;ChildRuleName (attributes) /&gt;
+ ...
+&lt;/RuleName&gt;
+</programlisting>
+
+
+<para>Rule specific attributes varies and are described in the
+following list.</para>
+
+<variablelist>
+<title>The Rules in Detail</title>
+
+<varlistentry>
+<term>DetectChar</term>
+<listitem>
+<para>Detect a single specific character. Commonly used for example to
+find the ends of quoted strings.</para>
+<programlisting>&lt;DetectChar char=&quot;(character)&quot; (common attributes) /&gt;</programlisting>
+<para>The <userinput>char</userinput> attribute defines the character
+to match.</para>
+</listitem>
+</varlistentry>
+
+<varlistentry>
+<term>Detect2Chars</term>
+<listitem>
+<para>Detect two specific characters in a defined order.</para>
+<programlisting>&lt;Detect2Chars char=&quot;(character)&quot; char1=&quot;(character)&quot; (common attributes) /&gt;</programlisting>
+<para>The <userinput>char</userinput> attribute defines the first character to match,
+<userinput>char1</userinput> the second.</para>
+</listitem>
+</varlistentry>
+
+<varlistentry>
+<term>AnyChar</term>
+<listitem>
+<para>Detect one character of a set of specified characters.</para>
+<programlisting>&lt;AnyChar String=&quot;(string)&quot; (common attributes) /&gt;</programlisting>
+<para>The <userinput>String</userinput> attribute defines the set of
+characters.</para>
+</listitem>
+</varlistentry>
+
+<varlistentry>
+<term>StringDetect</term>
+<listitem>
+<para>Detect an exact string.</para>
+<programlisting>&lt;StringDetect String=&quot;(string)&quot; [insensitive=&quot;TRUE|FALSE;&quot;] (common attributes) /&gt;</programlisting>
+<para>The <userinput>String</userinput> attribute defines the string
+to match. The <userinput>insensitive</userinput> attribute defaults to
+<userinput>FALSE</userinput> and is fed to the string comparison
+function. If the value is <userinput>TRUE</userinput> insensitive
+comparing is used.</para>
+</listitem>
+</varlistentry>
+
+<varlistentry>
+<term>RegExpr</term>
+<listitem>
+<para>Matches against a regular expression.</para>
+<programlisting>&lt;RegExpr String=&quot;(string)&quot; [insensitive=&quot;TRUE|FALSE;&quot;] [minimal=&quot;TRUE|FALSE&quot;] (common attributes) /&gt;</programlisting>
+<para>The <userinput>String</userinput> attribute defines the regular
+expression.</para>
+<para><userinput>insensitive</userinput> defaults to
+<userinput>FALSE</userinput> and is fed to the regular expression
+engine.</para>
+<para><userinput>minimal</userinput> defaults to
+<userinput>FALSE</userinput> and is fed to the regular expression
+engine.</para>
+<para>Because the rules are always matched against the beginning of
+the current string, a regular expression starting with a caret
+(<literal>^</literal>) indicates that the rule should only be
+matched against the start of a line.</para>
+<para>See <link linkend="regular-expressions">Regular
+Expressions</link> for more information on those.</para>
+</listitem>
+</varlistentry>
+
+<varlistentry>
+<term>Keyword</term>
+<listitem>
+<para>Detect a keyword from a specified list.</para>
+<programlisting>&lt;keyword String=&quot;(list name)&quot; (common attributes) /&gt;</programlisting>
+<para>The <userinput>String</userinput> attribute identifies the
+keyword list by name. A list with that name must exist.</para>
+</listitem>
+</varlistentry>
+
+<varlistentry>
+<term>Int</term>
+<listitem>
+<para>Detect an integer number.</para>
+<para><programlisting>&lt;Int (common attributes) /&gt;</programlisting></para>
+<para>This rule has no specific attributes. Child rules are typically
+used to detect combinations of <userinput>L</userinput> and
+<userinput>U</userinput> after the number, indicating the integer type
+in program code.</para>
+</listitem>
+</varlistentry>
+
+<varlistentry>
+<term>Float</term>
+<listitem>
+<para>Detect a floating point number.</para>
+<para><programlisting>&lt;Float (common attributes)
+/&gt;</programlisting></para>
+<para>This rule has no specific attributes.</para>
+</listitem>
+</varlistentry>
+
+<varlistentry>
+<term>HlCOct</term>
+<listitem>
+<para>Detect an octal point number representation.</para>
+<para><programlisting>&lt;HlCOct (common attributes) /&gt;</programlisting></para>
+<para>This rule has no specific attributes.</para>
+</listitem>
+</varlistentry>
+
+<varlistentry>
+<term>HlCHex</term>
+<listitem>
+<para>Detect a hexadecimal number representation.</para>
+<para><programlisting>&lt;Int (common attributes) /&gt;</programlisting></para>
+<para>This rule has no specific attributes.</para>
+</listitem>
+</varlistentry>
+
+<varlistentry>
+<term>HlCStringChar</term>
+<listitem>
+<para>Detect an escaped character.</para>
+<para><programlisting>&lt;HlCStringChar (common attributes)
+/&gt;</programlisting></para>
+<para>This rule has no specific attributes.</para>
+
+<para>It matches letteral representations of invisible characters
+commonly used in program code, for example <userinput>\n</userinput>
+(newline) or <userinput>\t</userinput> (TAB).</para>
+
+<para>The following characters will match if they follow a backslash
+(<literal>\</literal>):
+<userinput>abefnrtv&quot;'?</userinput>. Additionally, escaped
+hexadecimal numbers like for example <userinput>\xff</userinput> and
+escaped octal numbers, for example <userinput>\033</userinput> will
+match.</para>
+
+</listitem>
+</varlistentry>
+
+<varlistentry>
+<term>RangeDetect</term>
+<listitem>
+<para>Detect a string with defined start and end characters.</para>
+<programlisting>&lt;RangeDetect char=&quot;(character)&quot; char1=&quot;(character)&quot; (common attributes) /&gt;</programlisting>
+<para><userinput>char</userinput> defines the character starting the range,
+<userinput>char2</userinput> the character ending the range.</para>
+<para>Usefull to detect for example small quoted strings and the like, but note that
+since the hl engine works on one line at a time, this will not find strings spanning over a line break.</para>
+</listitem>
+</varlistentry>
+
+<varlistentry>
+<term>LineContinue</term>
+<listitem>
+<para>Matches at end of line.</para>
+<programlisting>&lt;LineContinue (common attributes) /&gt;</programlisting>
+<para>This rule has no specific attributes.</para>
+<para>This rule is usefull for switching context at end of line.</para>
+</listitem>
+</varlistentry>
+
+</variablelist>
+
+</sect1>
+
+</appendix>