Why does invalid html work

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Instant reply of any questions via email or live chat. Accurate, transparent quotes, no any hidden fees. Our Services. Contact Us. Get Social With me! Twitter Follow me on Twitter. Note that since the default value for aria-invalid is false , it is not strictly necessary to add the attribute to input. Note that it is not necessary to validate the fields immediately on blur; the application could wait until the form is submitted though this is not necessarily recommended.

The snippet below shows a very simple validation function, which only checks for the presence of a particular character in the real world, validation will likely be more sophisticated :. Note that the alert has the ARIA role attribute set to "alert. Forms: Using aria-invalid to identify failed fields. Vocabulary: false default No errors detected grammar A grammatical error has been detected. Any value not in this vocabulary should be treated as true.

Valid HTML is the only contract you have with the browser manufacturers. The HTML specification says how you should write documents, and how they should interpret them. In recent times, standards compliance of browsers has reached the point where, as long as you write valid code, all the major browsers should interpret your code the same way. This is almost always the case for HTML at least, with other standards having a few more differences in support here and there.

But what happens when you do pass a browser invalid code? If you leave a few errors in your page, the browser will fill in the gaps for you! Not so, as each browser does things differently. Consider the following code:. The errors are that 1 the strong element is incorrectly nested across multiple block elements, and 2 the anchor element is not closed.

When you try to display this code in different browsers, they interpret it in very different ways:. The bottom line is, avoid invalid markup in your pages if at all possible! Putting a URL into a validator to see whether the page is valid is easy; working out what is wrong and fixing the errors is sometimes not so easy, as the error messages can sometimes be a bit cryptic.

This simple page consists of three headings, three paragraphs, one hyperlink, and one unordered list. Open the W3C online validator in a new tab or window, so that you can switch between the validator and this article as you go through the example. Doing so should give you the result shown in Figure This may sound worrying, especially when we tell you that there are not 11 errors in the document!

This is because often an error at the top of the page will cascade, making the validator report more errors further down, as it looks like more elements are not closed or incorrectly nested.

You just have to think about what the error messages mean, look for obvious errors in the markup, and work from the top down.

Table 1 below shows all of the errors we fixed to make the page validate, along with our logic for working out what was wrong, and the fixes we applied to solve the problem. With these four errors fixed, the remaining seven disappear and the validator now gives a satisfying success message, as shown in Figure Below is the corrected version of the code; feel free to copy and paste it into a new page in your favorite editor.

You just need to keep your wits about you, code carefully, and remember what doctype your page is being validated against. Notice: The WebPlatform project, supported by various stewards between and , has been discontinued.