Idiomatic HTML Guidelines

1. Whitespace

Only one style should exist across the entire source of your code-base. Always be consistent in your use of whitespace. Use whitespace to improve readability.

  • Never mix spaces and tabs for indentation.
  • Preference: Tabs

2. Format

  • Always use lowercase tag and attribute names.
  • Write one discrete element per line.
  • Use one additional level of indentation for each nested element.
  • Use valueless boolean attributes (e.g. checked rather than checked="checked").
  • Always use double quotes to quote attribute values.
  • Omit the type attributes from link stylesheet, style and script elements.
  • Always include closing tags. <p>Some text</p> NOT <p>Some text
  • Don’t include a trailing slash in self-closing elements. <img src="#" alt="something"> NOT <img src="#" alt="something" />

Example:

<div class="tweet">
    <a href="path/to/somewhere">
        <img src="path/to/image.png" alt="">
    </a>
    <p>[tweet text]</p>
    <button disabled>Reply</button>
</div>

3. Attribute order

HTML attributes should be listed in an order that reflects the fact that class names are the primary interface through which CSS and JavaScript select elements.

  1. class
  2. id
  3. data-*
  4. Everything else

Example:

<a class="[value]" id="[value]" data-name="[value]" href="[url]">[text]</a>

4. Line Breaks

We highly recommend using <p> OR <span> to wrap all blocks of text over using <br> to control line breaks. You are not able to stlye the <br> tag which limits the control of the content on a page. Prefer the use of paragrphs or block level spans over breaks as you can not style a br tag. <p>Some text</p><p>Some More Text</p> OR <span class="something">Some text</span><span class="display-block-class">Some More Text</span> NOT Some text<br>Some More Text

Example with bad formated text:

<div class="content">

    <h3>
        This is a Title<br>
        <small>This is a subtitle</small>
    </h3>

    <p>
        Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.<br>
        Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.<br>
        Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur.<br>
        Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.<br>
    </p>

</div>

Example with good formated text:

.subtitle {
    display: block;
}

.no-margin {
    padding: 0;
    margin: 0;
}
<div class="content">

    <h3>
        This is a Title
        <small class="subtitle">This is a subtitle</small>
    </h3>

    <p class="no-margin">
        Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
    </p>
    <p class="no-margin">
        Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.
    </p>
    <p class="no-margin">
        Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur.
    </p>
    <p class="no-margin">
        Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
    </p>

</div>

5. Naming

Naming is hard, but very important. It’s a crucial part of the process of developing a maintainable code base, and ensuring that you have a relatively scalable interface between your HTML and CSS/JS.

  • Use clear, thoughtful, and appropriate names for HTML classes. The names should be informative both within HTML and CSS files.
  • Avoid systematic use of abbreviated class names. Don’t make things difficult to understand.

Example with bad names:

<div class="cb s-scr"></div>
.s-scr {
  overflow: auto;
}

.cb {
  background: #000;
}

Example with better names:

<div class="column-body is-scrollable"></div>
.is-scrollable {
    overflow: auto;
}

.column-body {
    background: #000;
}

6. Practical example

An example of various conventions.

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title>Document</title>
        <link rel="stylesheet" href="main.css">
        <script src="main.js"></script>
    </head>
    <body>
        <article class="post" id="1234">
            <time class="timestamp">March 15, 2012</time>
            <ul>
                <li>
                    <a href="[url]">[text]</a>
                    <img src="[url]" alt="[text]">
                </li>
                <li>
                    <a href="[url]">[text]</a>
                </li>
            </ul>

            <a class="link-complex" href="[url]">
                <span class="link-complex__target">[text]</span>
                [text]
            </a>

            <input value="text" readonly>
        </article>
    </body>
</html>