Are (non-void) self-closing tags valid in HTML5?

Distinguishing element types in HTML5

Void elements in HTML, like those cheeky <input>, <br>, and <img>, are inherently content-free and thus self-close. So, writing <img src="partying-cat.gif" /> (with an optional trailing slash) is like leading a conga line—totally groovy!

However, non-void elements—the ones often hosting content or junior elements—demand a cozy pairing of start and end tags. To illustrate, <ul><li>The bunny hops</li></ul>. It's like keeping your pair of fuzzy socks together in the laundry of web markup—essential.

Understanding XHTML's relationship with HTML5

For XHTML aficionados, the rules of the XML-based game demand that self-closing tags (<element />) only belong to empty elements. But when XHTML dons the text/html MIME-type mask and mingles in an HTML party, it should shake off the XML strictness and groove with standard HTML5 moves.

Rules for foreign elements in an HTML5 context

Foreign elements, such as the artsy <svg> and numerical <math> from SVG and MathML namespaces respectively, operate on XML terms within an HTML5 script. So, <path d="...it's a bird, it's a plane" /> within inline SVG on HTML5 page is as cool as a superhero landing.

Avoid self-closing blunders

Even though your friendly neighborhood Spider-Browser might fix syntax missteps like <div />, relying on this auto-correction feature is as risky as telling Thor his hammer looks kind of cute. Wield validation tools like the mighty Mjölnir—uh, I mean, W3C validator—to doom such errors.

The hide-and-seek of serialization and parsing

A deep dive into browser parsing versus content authoring rules can separate novices from ninjas. While browsers may mend HTML to form a congruent DOM despite off-beat markup, such leniency could result in off-key consequences, especially for symphonic documents.

HTML5's escapade from SGML

HTML5 is like a teenager rebelling against SGML (Standard Generalized Markup Language), which insisted that a closing angle bracket > be included but, in a quirky parental move, allowed it to be dropped under certain conditions. Nowadays, HTML5 aligns more with XML's rulebook—it knows when to be home before curfew.

Rolling out HTML as XML

In moments when you want to serve HTML as XML (application/xhtml+xml), tuning into the right MIME type radio station allows your browser to jam to the self-closing tags.

Staunchly standing for consistency

Though the trailing slash in self-closing void elements plays the optional character in the HTML5 drama (<br> can just as well be <br/>), sticking to a consistent self-closing syntax is like preparing an Oscar speech—it aids readability and prepares your code for the limelight in both HTML and XHTML scenes.

Error control central and validation vigil

HTML5 has its own rulebook of guidelines for content authoring and browser parsing. Flouting such prescriptions could lead to a chaotic DOM tree or rendering inconsistencies. It's like switching off Auto-Tune during a live performance—risky!

Ensuring consistent interplay

To ensure your code plays well with a variety of document types and future standards, it's a sound tactic to stick by HTML5 guidelines. This behavior aligns your projects with the current web trends and makes them easier to maintain.

Clarifying semantics

By following the HTML5 way of using tags, you provide a well-defined structure that translates to better readability and helps separate content from presentation. It makes your code easier to understand, like a well-structured novel instead of a mysterious code cipher.

Avoiding confusion

While using self-closing syntax for non-void elements might not cause immediate disasters, it could create chaotic riddles down the line. This adds confusion when working with other developers or integrating with third-party tools expecting HTML5 compliant code.