XHTML (Extensible HyperText Markup Language) is a stricter version of HTML that was rewritten to follow the rules of XML. In practice that means every tag has to be closed, elements must be properly nested, attributes need quotes, and everything is lowercase. It was an attempt to make web pages cleaner and more predictable.
Think of it as the difference between a casual text message and a formal contract. A text message still makes sense if you skip a comma or leave a sentence half-finished. A contract has rules: miss a signature and the whole thing is invalid. XHTML treated HTML like that contract, so a single unclosed tag could stop the entire page from displaying.
That strictness was the point and also the problem. It pushed developers toward tidier code, which paired well with CSS for styling. But on the real web, where pages are messy and browsers forgive a lot, the all-or-nothing approach felt heavy-handed. HTML5 eventually replaced it, keeping the good habits without the brittleness, and today XHTML mostly survives in older sites and a few specialised systems. There was a practical sting too. Served with the proper XML content type, a single stray ampersand or an unclosed image tag would show a raw error screen instead of the page, and visitors saw nothing. Many sites quietly sidestepped this by sending XHTML as plain HTML, which meant they got the syntax without the real benefit. That gap was a big reason it never won the browser compatibility fight. Internet Explorer 6, the dominant browser of the era, could not even parse true XHTML, so authors wrote strict markup that browsers then read loosely anyway.
At TopDevs we build with modern HTML5, but we still hold to the clean, well-formed markup that XHTML championed, because tidy code is easier to maintain, debug and keep working across browsers.
