182 lines
7.3 KiB
Java
182 lines
7.3 KiB
Java
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<!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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<link rel="icon" href="favicon.png" />
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<title>FAQ ▲ Prism</title>
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<link rel="stylesheet" href="style.css" />
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<link rel="stylesheet" href="themes/prism.css" data-noprefix />
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<style>
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#toc {
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display: block;
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position: static;
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max-width: 900px;
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font-size: 100%;
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opacity: 1;
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}
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</style>
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<script src="prefixfree.min.js"></script>
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<script>var _gaq = [['_setAccount', 'UA-33746269-1'], ['_trackPageview']];</script>
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<script src="https://www.google-analytics.com/ga.js" async></script>
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</head>
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<body>
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<header>
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<div class="intro" data-src="templates/header-main.html" data-type="text/html"></div>
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<h2>FAQ</h2>
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<p>Frequently Asked Questions, with a few Questions I want people to Frequently Ask.</p>
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</header>
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<section>
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<h1>This page doesn’t work in Opera!</h1>
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<p><strong>Prism works fine in Opera.</strong> However, this page might sometimes appear to not be working in Opera, due to the theme switcher triggering an Opera bug.
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This will be fixed soon.</p>
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</section>
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<section>
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<h1>Isn’t it bad to do syntax highlighting with regular expressions?</h1>
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<p>It is true that to correctly handle every possible case of syntax found in the wild, one would need to write a full-blown parser.
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However, in most web applications and websites a small error margin is usually acceptable and a rare highlighting failure is not the end of the world.
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A syntax highlighter based on regular expressions might only be accurate 99% of the time (the actual percentage is just a guess),
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but in exchange for the small error margin, it offers some very important benefits:
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<ul>
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<li>Smaller filesize. Proper parsers are very big.</li>
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<li>Extensibility. Authors can define new languages simply by knowing how to code regular expressions.
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Writing a correct, unambiguous BNF grammar is a task at least an order of magnitude harder.</li>
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<li>Graceful error recovery. Parsers fail on incorrect syntax, where regular expressions keep matching.</li>
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</ul>
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<p>For this reason, most syntax highlighters on the web and on desktop, are powered by regular expressions. This includes the internal syntax
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highlighters used by popular native applications like Espresso and Sublime Text, at the time of writing.
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Of course, not every regex-powered syntax highlighter is created equal. The number and type of failures can be vastly different, depending on
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the exact algorithm used. <a href="examples.html">Prism’s known failures are documented in the Examples section</a>.</p>
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</section>
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<section>
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<h1>Why is asynchronous highlighting disabled by default?</h1>
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<p>Web Workers are good for preventing syntax highlighting of really large code blocks from blocking the main UI thread.
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In most cases, you will want to highlight reasonably sized chunks of code, and this will not be needed.
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Furthermore, using Web Workers is actually <strong>slower</strong> than synchronously highlighting, due to the overhead of creating and terminating
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the Worker. It just appears faster in these cases because it doesn’t block the main thread.
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In addition, since Web Workers operate on files instead of objects, plugins that hook on core parts of Prism (e.g. modify language definitions)
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will not work unless included in the same file (using the builder in the <a href="download.html">Download</a> page will protect you from this pitfall).
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Lastly, Web Workers cannot interact with the DOM and most other APIs (e.g. the console), so they are notoriously hard to debug.
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</p>
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</section>
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<section>
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<h1>Why is pre-existing HTML stripped off?</h1>
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<p>Because it would complicate the code a lot, although it’s not a crucial feature for most people.
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If it’s very important to you, you can use the <a href="plugins/keep-markup/">Keep Markup plugin</a>.</p>
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</section>
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<section>
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<h1>If pre-existing HTML is stripped off, how can I highlight certain parts of the code?</h1>
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<p>There is a number of ways around it. You can always break the block of code into multiple parts, and wrap the HTML around it (or just use a <code>.highlight</code> class).
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You can see an example of this in action at the “<a href="index.html#basic-usage">Basic usage</a>” section of the homepage.</p>
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<p>Another way around the limitation is to use the <a href="plugins/line-highlight/">Line Highlght plugin</a>, to highlight and link to specific lines and/or line ranges.
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</section>
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<section>
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<h1>How do I know which tokens I can style for every language?</h1>
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<p>Every token that is highlighted gets two classes: <code>token</code> and a class with the token type (e.g. <code>comment</code>).
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You can find the different types of tokens either by looking at the keys of the object defining the language or by running this snippet in the console:
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<pre><code class="language-javascript">function printTokens(o, prefix) { for (var i in o) { console.log((prefix? prefix + ' > ' : '') + i); if (o[i].inside) printTokens(o[i].inside, (prefix? prefix + ' > ' : '') + i); } };</code></pre>
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<p>Then you can use the function for every language you want to examine. For example, markup:</p>
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<pre><code class="language-javascript">printTokens(Prism.languages.markup);</code></pre>
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<p>which outputs:</p>
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<pre>comment
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prolog
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doctype
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script
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script > tag
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script > tag > tag
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script > tag > tag > punctuation
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script > tag > tag > namespace
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script > tag > attr-value
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script > tag > attr-value > punctuation
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script > tag > punctuation
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script > tag > attr-name
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script > tag > attr-name > namespace
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script > rest
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style
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style > tag
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style > tag > tag
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style > tag > tag > punctuation
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style > tag > tag > namespace
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style > tag > attr-value
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style > tag > attr-value > punctuation
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style > tag > punctuation
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style > tag > attr-name
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style > tag > attr-name > namespace
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style > rest
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cdata
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tag
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tag > tag
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tag > tag > punctuation
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tag > tag > namespace
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tag > attr-value
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tag > attr-value > punctuation
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tag > punctuation
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tag > attr-name
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tag > attr-name > namespace
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entity</pre>
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</section>
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<section>
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<h1>How can I use different highlighting for tokens with the same name in different languages?</h1>
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<p>Just use a descendant selector, that includes the language class. The default <code>prism.css</code> does this, to have different colors for
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JavaScript strings (which are very common) and CSS strings (which are relatively rare). Here’s that code, simplified to illustrate the technique:
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<pre><code class="language-css">
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.token.string {
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color: #690;
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}
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.language-css .token.string,
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.style .token.string {
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color: #a67f59;
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}</code></pre>
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<p>Abbreviated language classes (e.g. <code>lang-css</code>) will be converted to their extended forms, so you don’t need to account for them.</p>
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<p>The same technique can be used to differentiate XML tag namespaces from attribute namespaces:</p>
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<pre><code class="language-css">.tag > .token.namespace {
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color: #b37298;
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}
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.attr-name > .token.namespace {
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color: #ab6;
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}</code></pre>
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</section>
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<footer data-src="templates/footer.html" data-type="text/html"></footer>
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<script src="prism.js"></script>
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<script src="utopia.js"></script>
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<script>
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$$('section > h1').forEach(function (h1) {
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$u.element.create('p', {
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contents: {
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tag: 'a',
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properties: {
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href: '#toc'
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},
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contents: '↑ Back to top'
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},
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inside: h1.parentNode
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});
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});
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</script>
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<script src="components.js"></script>
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<script src="code.js"></script>
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</body>
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</html>
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