Debugging common HTML validation errors.
Jul 03, 2025 am 02:41 AM

1. Missing required attributes
<p> Some tags require specific attributes to pass verification, such as<img src="/static/imghw/default1.png" data-src="https://img.php.cn/upload/article/000/000/000/175148166575363.jpeg" class="lazy" alt="Debugging common HTML validation errors." >
must have src
and alt
, and <a></a>
must have href
. If you miss these properties, the validator will report an error.

- See the specifications and requirements of each label clearly
- Pay special attention to form elements and multimedia related tags, which usually require strict attributes.
- For example, the
<input>
tag should contain at leasttype
andname

<!-- Error writing--> <img src="/static/imghw/default1.png" data-src="photo.jpg" class="lazy" alt="Debugging common HTML validation errors." > <!-- Correct writing method--> <img src="/static/imghw/default1.png" data-src="photo.jpg" class="lazy" alt="Description Picture Content">
2. Improperly nested tags
<p> Label nesting errors are common problems for beginners, such as applying<div>
in <p>
, or opening a new label if you forget to close a tag.<p> Why errors occur:- HTML structure is not clear, especially when multi-layer nesting is more likely to get confused
- If the editor does not have automatic completion or indent reminder, it is easy to ignore it
- Close it immediately after writing a tag and add content to it
- Use the automatic formatting feature of the code editor to check the structure
- Common error combinations such as
<p><div>...
<div>
is a block-level element and cannot be placed in <p>
3. Invalid or deprecated tags
<p> Sometimes we accidentally use labels that have been eliminated, such as<center>
, <font>
, or some old labels that are not supported by HTML5.<p> How to determine if the tag is invalid:- Check the specific prompts given by the validator, and usually say "Element is obsolete"
- Refer to the official MDN document to confirm the tag status
- Rewrite with modern alternatives, such as controlling styles with CSS instead of relying on old tags
<!-- Obsolete writing--> <center>Chinese characters</center> <!-- Recommended writing method--> <div style="text-align: center;">Chinese characters</div>
4. Character encoding issues
<p> The page appears garbled, or the validator prompts "character encoding" error, usually the correct character set is not set.<p> The solution is simple:- Add this line to
<head>
:<meta charset="UTF-8">
- Make sure your file is saved as UTF-8 encoding (most editors can set)
- This is especially important if you use Chinese or other non-English characters <p> Basically that's it. Although HTML verification errors may seem annoying, they are mostly small structural or syntax problems that can be quickly fixed as long as you pay attention.
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