A parser error happens when the browser has to recover from malformed markup. A validator warning or error reports a rule problem, even when the browser still displays something.
What You Need to Know
Browsers try hard to recover, so a page looking correct is not proof that the HTML is valid. Validation finds mistakes before they become confusing bugs.
Browsers can repair malformed HTML into a DOM that differs from the source. Validators report conformance errors even when the screen looks reasonable.
The goal is not to collect as many tags as possible. Pick the element that best describes what the content really is.
Example: See It in Action
This example keeps the idea small. Copy it carefully, then follow the explanation instead of guessing what the browser will do.
The first line below is intentionally incorrect. Find the nesting mistake before reading the corrected version.
<p><strong>Important message</p></strong>
<p>Put closing tags in the proper order.</p>
<p>Correct: <strong>Important message</strong>
</p>Let’s Understand the Example
- A p groups a paragraph of related text. Start another paragraph for a new thought.
- Strong marks text as particularly important. It means more than simply making words bold.
Look for the text “Important message” in the page. If the visible result surprises you, inspect the rendered elements to see what the browser actually built.
What Should You See?
The page should include “Important message”. If it looks different from what you expected, open developer tools and compare the source with the elements the browser created.
Try removing one piece of markup in a scratch copy, refresh the page, and compare the behavior. This is often the fastest way to understand what that piece contributes.
Try It Yourself
- Repair the incorrect nesting in the example and check the result in a validator.
- Save your changes, open or refresh the page, and compare the result with the original example.
- Tell a friend what your change did. If you are not sure, undo it, refresh the page, and compare.
Common Beginner Mistakes
- Ignoring a validation error because a page appears normal in one browser.
- Avoid picking tags just for their default bold, italic or spaced appearance. Use CSS for presentation.
Key Takeaways
- A parser error happens when the browser has to recover from malformed markup.
- A p groups a paragraph of related text. Start another paragraph for a new thought.
- Browsers can repair malformed HTML into a DOM that differs from the source. Validators report conformance errors even when the screen looks reasonable.