The main differences between HTML and XHTML are syntax strictness, file type processing and error handling methods. HTML is more flexible, allowing tags to be mixed with upper and lowercase, tags can not be closed, and attribute values ??do not require quotation marks; while XHTML follows XML rules, requiring all tags to be lowercase, must be closed, and attribute values ??need to be quoted. HTML files are usually transferred in the text/html MIME type and are parsed using an HTML parser; XHTML should be transferred in the application/xhtml xml type, otherwise it may lead to parsing errors. HTML is tolerant of errors, and the browser will try its best to render; XHTML will stop rendering and report an error due to syntax errors. Although XHTML was once regarded as the future direction, HTML5 has become mainstream today. It combines the advantages of HTML and XHTML, while avoiding the forced strict XML syntax, which is more suitable for general web development.

HTML and XHTML are both markup languages ??used for structuring web content, but they have distinct rules and purposes that affect how developers write and maintain code. The main difference lies in their syntax and parsing requirements — HTML is more forgiving, while XHTML is stricter and follow XML rules.

Syntax Strictness

One of the most noticeable differences is how strict each format is about syntax.

<li> HTML allows for more flexibility. Tags can be written in uppercase or lowercase, some tags can be left unclosed (like <li> or <p></p> ), and attribute values ??don't always need quotes. <li> XHTML , on the other hand, requires well-formed documents. All tags must be lowercase, every opened tag must be closed properly (eg, <br> instead of <br> ), and all attributes must have quotes around their values.

This strictness makes XHTML documents easier to process with XML tools but also adds more overhead when writing or maintaining code manually.

File Type and MIME Handling

Another key distinction is how browsers handle files based on their type.

<li> HTML files are usually served with the text/html MIME type, which means browsers will parse them using an HTML parser. <li> XHTML should be served as application/xhtml xml . If you serve XHTML with the HTML MIME type, older browsers might not interpret it correctly, leading to rendering issues or broken pages.

In practice, this means that if you're using XHTML, your server configuration needs to support the correct MIME type — something many developers prefer to avoid due to compatibility concerns.

Error Handling

How errors are handled is another practical difference that affects debugging.

<li> In HTML , browsers tend to be lenient. Even if your markup has errors, browsers often try to render the page anyway. This can hide problems and make debugging trickier. <li> With XHTML , any syntax error usually causes the browser to stop rendering and display an error message. While this can be frustrating during development, it helps catch issues early and ensures cleaner code overall.

Tooling and Usage Today

While XHTML was once promoted as the future of web markup, its adoption never fully took off.

<li> Most modern websites use HTML5 , which blends the best parts of HTML and XHTML without enforcing XML's strict syntax. <li> XHTML is still relevant in specific environments like embedded systems or applications that require XML processing, but for general web development, it's largely been replaced by HTML5 with stricter coding practices encouraged through linters and validators.

So unless you're working in a context that specifically needs XML parsing, sticking with HTML5 and writing clean, semantic markup is usually the better choice.

Basically that's it.

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