234 lines
18 KiB
HTML
234 lines
18 KiB
HTML
<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="utf-8" />
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<meta name="viewport" content="width=device-width, initial-scale=1.0" />
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<meta
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name="description"
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content="kdl is a document language, mostly based on SDLang, with xml-like semantics that looks like you're invoking a bunch of CLI commands!"
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/>
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<title>The KDL Document Language</title>
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<link rel="stylesheet" href="/styles/global.css" />
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</head>
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<body>
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<main><header class="py-10 bg-gray-300">
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<h1 class="text-4xl text-center">The KDL Document Language</h1>
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</header>
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<section class="kdl-section" id="description">
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<p>KDL is a document language with xml-like semantics that looks like you're
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invoking a bunch of CLI commands! It's meant to be used both as a
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serialization format and a configuration language, much like JSON, YAML, or
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XML.</p>
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<p>There's a living
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<a href="https://github.com/kdl-org/kdl/blob/main/SPEC.md">specification</a>, as well as
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various <a href="#implementations">implementations</a>. You can also check out the
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<a href="#faq">FAQ</a> to answer all your burning questions!</p>
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<p>The language is based on <a href="https://sdlang.org">SDLang</a>, with a number of
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modifications and clarifications on its syntax and behavior.</p>
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</section>
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<section class="kdl-section" id="overview">
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<h2>Overview</h2>
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<h3>Basics</h3>
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<p>A KDL node is a node name, followed by zero or more "arguments", and
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children.</p>
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<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">title</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">"Hello, World"</span></span></code></pre>
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<p>You can also have multiple values in a single node!</p>
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<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">bookmarks</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">12</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">15</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">188</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">1234</span></span></code></pre>
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<p>Nodes can have properties.</p>
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<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">author</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">"Alex Monad"</span><span style="color: #D8DEE9FF"> </span><span style="color: #8FBCBB">email</span><span style="color: #ECEFF4">=</span><span style="color: #A3BE8C">"alex@example.com"</span><span style="color: #D8DEE9FF"> </span><span style="color: #8FBCBB">active</span><span style="color: #ECEFF4">=</span><span style="color: #81A1C1">true</span></span></code></pre>
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<p>And they can have nested child nodes, too!</p>
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<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">contents</span><span style="color: #D8DEE9FF"> {</span></span>
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<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #81A1C1">section</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">"First section"</span><span style="color: #D8DEE9FF"> {</span></span>
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<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #81A1C1">paragraph</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">"This is the first paragraph"</span></span>
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<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #81A1C1">paragraph</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">"This is the second paragraph"</span></span>
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<span class="line"><span style="color: #D8DEE9FF"> }</span></span>
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<span class="line"><span style="color: #D8DEE9FF">}</span></span></code></pre>
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<p>Nodes without children are terminated by a newline, a semicolon, or the end of
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a file stream:</p>
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<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">node1</span><span style="color: #D8DEE9FF">; </span><span style="color: #81A1C1">node2</span><span style="color: #D8DEE9FF">; </span><span style="color: #81A1C1">node3</span><span style="color: #D8DEE9FF">;</span></span></code></pre>
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<h3>Values</h3>
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<p>KDL supports 4 data types:</p>
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<ul>
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<li>Strings: <code>"hello world"</code></li>
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<li>Numbers: <code>123.45</code></li>
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<li>Booleans: <code>true</code> and <code>false</code></li>
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<li>Null: <code>null</code></li>
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</ul>
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<h4>Strings</h4>
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<p>It supports two different formats for string input: escaped and raw.</p>
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<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">node</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">"this</span><span style="color: #EBCB8B">\n</span><span style="color: #A3BE8C">has</span><span style="color: #EBCB8B">\t</span><span style="color: #A3BE8C">escapes"</span></span>
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<span class="line"><span style="color: #81A1C1">other</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">r"C:\Users\zkat\"</span></span></code></pre>
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<p>Both types of string can be multiline as-is, without a different syntax:</p>
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<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">string</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">"my</span></span>
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<span class="line"><span style="color: #A3BE8C">multiline</span></span>
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<span class="line"><span style="color: #A3BE8C">value"</span></span></code></pre>
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<p>And for raw strings, you can add any number of # after the r and the last " to
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disambiguate literal " characters:</p>
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<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">other-raw</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">r#"hello"world"#</span></span></code></pre>
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<h4>Numbers</h4>
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<p>There's 4 ways to represent numbers in KDL. KDL does not prescribe any
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representation for these numbers, and it's entirely up to individual
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implementations whether to represent all numbers with a single type, or to
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have different representations for different forms.</p>
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<p>KDL has regular decimal-radix numbers, with optional decimal part, as well as
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an optional exponent.</p>
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<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">num</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">1.234e-42</span></span></code></pre>
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<p>And using the appropriate prefix, you can also enter hexadecimal, octal, and
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binary literals:</p>
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<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">my-hex</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">0xdeadbeef</span></span>
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<span class="line"><span style="color: #81A1C1">my-octal</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">0o755</span></span>
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<span class="line"><span style="color: #81A1C1">my-binary</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">0b10101101</span></span></code></pre>
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<p>Finally, all numbers can have underscores to help readability:</p>
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<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">bignum</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">1_000_000</span></span></code></pre>
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<h3>Comments</h3>
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<p>KDL supports C-style comments, both line-based and multiline. Multiline
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comments can be nested.</p>
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<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #616E88">// C style</span></span>
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<span class="line"><span style="color: #616E88">/*</span></span>
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<span class="line"><span style="color: #616E88">C style multiline</span></span>
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<span class="line"><span style="color: #616E88">*/</span></span>
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<span class="line"><span style="color: #81A1C1">tag</span><span style="color: #D8DEE9FF"> </span><span style="color: #616E88">/*foo=true*/</span><span style="color: #D8DEE9FF"> </span><span style="color: #8FBCBB">bar</span><span style="color: #ECEFF4">=</span><span style="color: #81A1C1">false</span></span>
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<span class="line"><span style="color: #616E88">/*/*</span></span>
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<span class="line"><span style="color: #616E88">hello</span></span>
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<span class="line"><span style="color: #616E88">*/*/</span></span></code></pre>
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<p>On top of that, KDL supports <code>/-</code> "slashdash" comments, which can be used to
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comment out individual nodes, arguments, or children:</p>
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<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #616E88">// This entire node and its children are all commented out.</span></span>
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<span class="line"><span style="color: #616E88">/-mynode "foo" key=1 {</span></span>
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<span class="line"><span style="color: #616E88"> a</span></span>
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<span class="line"><span style="color: #616E88"> b</span></span>
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<span class="line"><span style="color: #616E88"> c</span></span>
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<span class="line"><span style="color: #616E88">}</span></span>
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<span class="line"><span style="color: #81A1C1">mynode</span><span style="color: #D8DEE9FF"> </span><span style="color: #616E88">/-"commented" </span><span style="color: #A3BE8C">"not commented"</span><span style="color: #D8DEE9FF"> </span><span style="color: #616E88">/-key="value" /-{</span></span>
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<span class="line"><span style="color: #616E88"> a</span></span>
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<span class="line"><span style="color: #616E88"> b</span></span>
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<span class="line"><span style="color: #616E88">}</span></span></code></pre>
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<h3>More Details</h3>
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<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #616E88">// Nodes can be separated into multiple lines</span></span>
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<span class="line"><span style="color: #81A1C1">title</span><span style="color: #D8DEE9FF"> \</span></span>
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<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">"Some title"</span></span>
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<span class="line"><span style="color: #616E88">// Files must be utf8 encoded!</span></span>
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<span class="line"><span style="color: #81A1C1">smile</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">"😁"</span></span>
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<span class="line"><span style="color: #616E88">// Instead of anonymous nodes, nodes and properties can be wrapped</span></span>
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<span class="line"><span style="color: #616E88">// in "" for arbitrary node names.</span></span>
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<span class="line"><span style="color: #A3BE8C">"!@#$@$%Q#$%~@!40"</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">"1.2.3"</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">"!!!!!"</span><span style="color: #D8DEE9FF">=</span><span style="color: #81A1C1">true</span></span>
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<span class="line"><span style="color: #616E88">// The following is a legal bare identifier:</span></span>
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<span class="line"><span style="color: #81A1C1">foo123~!@#$%^&*.</span><span style="color: #D8DEE9FF">:'</span><span style="color: #81A1C1">|/</span><span style="color: #D8DEE9FF">?</span><span style="color: #81A1C1">+</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">"weeee"</span></span>
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<span class="line"><span style="color: #616E88">// And you can also use unicode!</span></span>
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<span class="line"><span style="color: #81A1C1">ノード</span><span style="color: #D8DEE9FF"> </span><span style="color: #81A1C1">お名前</span><span style="color: #D8DEE9FF">＝</span><span style="color: #A3BE8C">"☜(ﾟヮﾟ☜)"</span></span>
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<span class="line"><span style="color: #616E88">// kdl specifically allows properties and values to be</span></span>
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<span class="line"><span style="color: #616E88">// interspersed with each other, much like CLI commands.</span></span>
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<span class="line"><span style="color: #81A1C1">foo</span><span style="color: #D8DEE9FF"> </span><span style="color: #8FBCBB">bar</span><span style="color: #ECEFF4">=</span><span style="color: #81A1C1">true</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">"baz"</span><span style="color: #D8DEE9FF"> </span><span style="color: #8FBCBB">quux</span><span style="color: #ECEFF4">=</span><span style="color: #81A1C1">false</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">1</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">2</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">3</span></span></code></pre>
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</section>
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<section class="kdl-section" id="implementations">
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<h2>Implementations</h2>
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<ul>
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<li>Rust: <a href="https://github.com/kdl-org/kdl-rs">kdl-rs</a></li>
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<li>JavaScript: <a href="https://github.com/kdl-org/kdljs">kdljs</a></li>
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<li>Ruby: <a href="https://github.com/jellymann/kdl-rb">kdl-rb</a></li>
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</ul>
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<h2>Editor Support</h2>
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<ul>
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<li><a href="https://marketplace.visualstudio.com/items?itemName=kdl-org.kdl&ssr=false#review-details">VS Code</a></li>
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</ul>
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</section>
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<section class="kdl-section" id="design-and-discussion">
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<h2>Design and Discussion</h2>
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<p>KDL is still extremely new, and discussion about the format should happen over
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on the <a href="https://github.com/kdl-org/kdl/discussions">discussions</a> page in the
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Github repo. Feel free to jump in and give us your 2 cents!</p>
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</section>
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<section class="kdl-section" id="design-principles">
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<h2>Design Principles</h2>
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<ol>
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<li>Maintainability</li>
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<li>Flexibility</li>
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<li>Cognitive simplicity and Learnability</li>
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<li>Ease of de/serialization</li>
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<li>Ease of implementation</li>
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</ol>
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</section>
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<section class="kdl-section" id="faq">
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<h2>FAQ</h2>
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<h4>Why yet another document language?</h4>
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<p>Because nothing out there felt quite right. The closest one I found was
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SDLang, but that had some design choices I disagreed with.</p>
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<h4>Ok, then, why not SDLang?</h4>
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<p>SDLang is designed for use cases that are not interesting to me, but are very
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relevant to the D-lang community. KDL is very similar in many ways, but is
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different in the following ways:</p>
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<ul>
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<li>The grammar and expected semantics are <a href="https://github.com/kdl-org/kdl/blob/main/SPEC.md">well-defined and specified</a>.</li>
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<li>There is only one "number" type. KDL does not prescribe representations.</li>
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<li>Slashdash (<code>/-</code>) comments are great and useful!</li>
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<li>I am not interested in having first-class date types, and SDLang's are very
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non-standard.</li>
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<li>Values and properties can be interspersed with each other, rather than one
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having to follow the other.</li>
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<li>KDL does not have a first-class binary data type. Just use strings with base64.</li>
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<li>All strings in KDL are multi-line, and raw strings are written with
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Rust-style syntax (<code>r"foo"</code>), instead of backticks.</li>
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<li>KDL identifiers can use UTF-8 and are much more lax about symbols than SDLang.</li>
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<li>KDL does not support "anonymous" nodes.</li>
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<li>Instead, KDL supports arbitrary identifiers for node names and attribute
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names, meaning you can use arbitrary strings for those: <code>"123" "value"=1</code> is
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a valid node, for example. This makes it easier to use KDL for
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representing arbitrary key/value pairs.</li>
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</ul>
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<h4>Have you seen that one XKCD comic about standards?</h4>
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<p>Yes. I have. Please stop linking me to it.</p>
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<h4>What about YAML?</h4>
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<p>YAML is a great, widespread language. Unlike KDL, which is node-based (like
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XML or HTML), it's based on map and array data structures, which can provide
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an easier serialization experience in some cases.</p>
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<p>At the same time, YAML can be ambiguous about what types the data written into
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it is. There's also a persistent issue where very large YAML files become
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unmanageable, especially due to the significant indentation feature.</p>
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<p>KDL is designed to avoid these particular pitfalls by always being explicit
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about types, and having clearly-delimited scope (and the ability to
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auto-indent/auto-format). Syntax errors are easier to catch, and large files
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are (hopefully!) much more manageable.</p>
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<h4>What about JSON?</h4>
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<p>JSON is a great serialization language, but it can be very difficult to use as
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a human configuration language. This is largely due to its very specific, very
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strict syntax, as well as its lack of support for comments.</p>
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<p>KDL, on the other hand, has great comment support, and has a much more
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forgiving syntax without being so flexible as to allow certain classes of
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unfortunate mistakes. It also has much more flexibility around how to
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represent data.</p>
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<h4>What about TOML?</h4>
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<p>It nests very poorly. It doesn't fare well with large files.</p>
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<h4>What about XML?</h4>
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<p>XML is actually pretty fantastic, and has long been a standard for data
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exchange across many industries. At the same time, XML is known to be very
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verbose, and editing it involves writing (and updating) matching tags. Another
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large pitfall with XML is its lack of direct support for arbitrary string
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key/value pairs, so what would be a simple <code>foo: x</code> in some languages has to
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be represented as <code><entry name="foo" value="x" /></code> or something similar. XML
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also functions great as a <strong>markup</strong> language. That is, it is easy to
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intersperse with text, like HTML.</p>
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<p>KDL, just like XML, is a node/element-based language, but with much more
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lightweight syntax. It also adds the ability to apply anonymous values
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directly to a node, rather than as children. That is, <code>nodename 1 2 3</code> instead
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of <code><element><child>1</child><child>2</child>(etc)</element></code>. This can make
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it much more manageable and readable as a human configuration language, and is
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also less verbose when exchanging documents across APIs!</p>
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<p>Finally, KDL is <strong>not</strong> a markup language. XML or HTML do a much better job of
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"marking up" a text document with special tags, although KDL can still be
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useful for templating engines that want to be more strict about text
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fragments.</p>
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</section>
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</main>
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</body>
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</html>
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