HTML Guide
A <style> start tag has been found in an unexpected place in the document structure. Check that the <style> section appears within the <head> section.
Although in general it’s better to put your styles in external stylesheets and apply them using <link> elements, CSS styles can also be included inside a document using the <style> tag. In this case, it should be placed within the <head> section, like in this example:
<!DOCTYPE html>
<html>
<head>
<title>Test</title>
<style>
p {
color: #26b72b;
}
</style>
</head>
<body>
<p>This text will be green.</p>
</body>
</html>A <td> or <th> element has a colspan attribute value that extends beyond the total number of columns defined in the <tbody> section.
HTML tables must have rows with a consistent number of columns within each <thead>, <tbody>, or <tfoot> group. If a cell uses the colspan attribute to span more columns than exist in the current row group, the table becomes semantically incorrect and fails validation.
Example of the Issue
<table>
<tbody>
<tr>
<td>Cell 1</td>
<td>Cell 2</td>
</tr>
<tr>
<td colspan="3">Too wide</td> <!-- Invalid: colspan="3" but only 2 columns in tbody -->
</tr>
</tbody>
</table>How to Fix
Ensure that the maximum number of columns in any row (considering colspan) within a <tbody> does not exceed the columns defined by the longest row in that group.
Corrected Example
<table>
<tbody>
<tr>
<td>Cell 1</td>
<td>Cell 2</td>
<td>Cell 3</td>
</tr>
<tr>
<td colspan="3">Spans all columns</td>
</tr>
</tbody>
</table>Or, if you only need two columns:
<table>
<tbody>
<tr>
<td>Cell 1</td>
<td>Cell 2</td>
</tr>
<tr>
<td colspan="2">Spans two columns</td>
</tr>
</tbody>
</table>Adjust the column count by either increasing the number of cells in each row or reducing the value of colspan as appropriate for your table structure.
Ensure each column in your table has at least one <td> or <th> cell starting in it. This error often occurs when using the colspan or rowspan attributes incorrectly.
Example of correct usage:
<table>
<tr>
<th>Header 1</th>
<th>Header 2</th>
</tr>
<tr>
<td>Row 1, Cell 1</td>
<td>Row 1, Cell 2</td>
</tr>
<tr>
<td>Row 2, Cell 1</td>
<td>Row 2, Cell 2</td>
</tr>
</table>Incorrect usage example:
<table>
<tr>
<th>Header 1</th>
<th>Header 2</th>
</tr>
<tr>
<td colspan="2">Row 1, Cell 1</td>
</tr>
<tr>
<td>Row 2, Cell 1</td>
<!-- Missing cell in column 2 -->
</tr>
</table>The corrected version ensuring each column has a starting cell:
<table>
<tr>
<th>Header 1</th>
<th>Header 2</th>
</tr>
<tr>
<td colspan="2">Row 1, spanning both columns</td>
</tr>
<tr>
<td>Row 2, Cell 1</td>
<td>Row 2, Cell 2</td>
</tr>
</table>A <table> contains an incoherent number of cells on one of its columns. Check the structure of the table to find the invalid column.
Example of a valid table that defines in its header that the first column is 2 cells wide:
<table>
<thead>
<tr>
<th colspan="2">The table header</th>
</tr>
</thead>
<tbody>
<tr>
<td>The table body</td>
<td>with two columns</td>
</tr>
</tbody>
</table>This same table with an empty body will be invalid because the table header cannot match any body columns:
<table>
<thead>
<tr>
<th colspan="2">The table header</th>
</tr>
</thead>
<tbody>
</tbody>
</table>A <table> contains an incoherent number of columns on one of its rows. Check the structure of the table to find the invalid row.
For example, in the following table, the first <tr> row defines that it’s 2 columns wide, but the second <tr> row tries to use 5 columns by means of a colspan attribute:
<table>
<!-- This first row sets the table as 2 columns wide -->
<tr>
<td>First</td>
<td>Second</td>
</tr>
<!-- This second row tries to use 5 columns -->
<tr>
<td colspan="5">Wrong</td>
</tr>
</table><iframe> tags are used to embed another document within the current document. To indicate the contents of that nested document, you can either use the src attribute with an URL, or directly provide the contents with the srcdoc attribute. Examples:
<!-- This will embed a document by its URL -->
<iframe src="https://example.com"></iframe>
<!-- This will embed the contents provided in the srcdoc attribute -->
<iframe srcdoc="<p>some content</p>"></iframe>
<!-- This is invalid -->
<iframe><p>some content</p></iframe>This W3C HTML Validator issue indicates that you’ve placed text content directly inside a <select> element. According to the HTML specification, a <select> element can only contain <option> or <optgroup> elements, and no direct text nodes.
Here’s how to resolve this issue:
Steps to Fix:
- Remove Text Nodes: Ensure that you remove any text that exists directly inside the <select> tags.
- Use <option> Elements: If you want to display text as an option, use <option> tags for each selectable item.
Example of Incorrect Usage:
Here’s an example that generates the validator issue:
<select>
Please select an option:
<option value="1">Option 1</option>
<option value="2">Option 2</option>
</select>Corrected Example:
Here’s how to correct this by moving the text outside of the <select> element:
<label for="options">Please select an option:</label>
<select id="options">
<option value="1">Option 1</option>
<option value="2">Option 2</option>
</select>Summary:
- Always wrap any instructional or descriptive text outside of the <select> element.
- Use <option> tags to define the choices within the <select>.
The <ul> element is used to define unordered lists, where each element must be contained within a <li> element, like in this example:
<ul>
<li>first element</li>
<li>second element</li>
<li>third element</li>
</ul>Ensure that there’s no content inside the <ul> element that is not contained within a <li> element.
Sometimes this error comes when trying to give a title to the list, for example:
<ul>
Fruits
<li>Apple</li>
<li>Orange</li>
</ul>Instead, that title text should be outside the list, like:
<span>Fruits</span>
<ul>
<li>Apple</li>
<li>Orange</li>
</ul>Other times, this can come as the concatenation of <li> elements which results in something like:
<ul>
<li>First item</li>
<li>Second item</li>
<li>Third item</li>
</ul>Note how in this case that used to join the <li> is causing the problem, as it’s content that is not contained by a <li> element, as required by the <ul> element.
Read about Normalization in HTML and CSS.
The <th> HTML element defines a cell as a header of a group of table cells, and must appear within a <tr> element.
In the following example for a simple table, the first <tr> contains two <th> header cells naming the values for each column:
<table>
<tr>
<th>Name</th>
<th>Age</th>
</tr>
<tr>
<td>Liza</td>
<td>49</td>
<tr>
<tr>
<td>Joe</td>
<td>47</td>
</tr>
</table>The old <acronym> element in previous versions is now obsolete, in HTML5 you must use <abbr> instead.
<td> elements no longer accept an align attribute. This can be achieved using CSS like this:
<td style="text-align:center;">content</td>The aria-controls attribute identifies an element or elements in the same document whose contents or presence are controlled by the current element. It must point to existing elements by their ID. Check that the IDs contained in that property exist within the same document.
ARIA can express semantic relationships between elements that extend the standard parent/child connection, such as a custom scrollbar that controls a specific region, for example:
<div role="scrollbar" aria-controls="main"></div>
<div id="main">
. . .
</div>The aria-describedby attribute is used to indicate the IDs of the elements that describe the object. It should reference an existing ID on the same document, but that id was not found.
The aria-hidden attribute is redundat on an input of type hidden, so it should be removed.
Example:
<!-- Instead of this... -->
<input type="hidden" aria-hidden="true" id="month" value="10" />
<!-- You can just use this -->
<input type="hidden" id="month" value="10" />The aria-labelledby attribute establishes relationships between objects and their label(s), and its value should be one or more element IDs. It should reference an existing ID on the same document, but that id was not found.
The aria-owns attribute contains an ID reference that does not match any element in the same document.
According to the ARIA specification and the WHATWG HTML standard, the value of the aria-owns attribute must be a space-separated list of IDs of elements that exist in the same DOM document. This attribute is meant to modify the accessibility tree by creating relationships not present in the DOM structure, but all referenced elements must be part of the same document. If an ID in the aria-owns attribute does not match any element, is in another document (such as an iframe), or contains a typo, validation will fail.
Common reasons for this issue:
- Referencing a nonexistent ID.
- Referencing an ID from another document (e.g., across iframes).
- Typos in the ID value.
Correct usage:
<div id="container" aria-owns="owned-element">
<p>Container</p>
</div>
<div id="owned-element">
<p>Owned by container (in accessibility tree)</p>
</div>Incorrect usage (missing or cross-document ID):
<div id="parent" aria-owns="child"></div>
<!-- Missing <div id="child"> or 'child' exists in a different frame/document -->To fix the issue, ensure that all IDs referenced in aria-owns correspond to elements present in the same document.
Complete valid example:
<!DOCTYPE html>
<html lang="en">
<head>
<title>aria-owns Example</title>
</head>
<body>
<div id="menu" aria-owns="item1 item2">
Main menu (accessibility tree owner)
</div>
<div id="item1">
Menu item 1
</div>
<div id="item2">
Menu item 2
</div>
</body>
</html>The article role indicates a section of a page that could easily stand on its own on a page, in a document, or on a website, is implicit when using the <article> tag.
This role indicates a section of a page that could easily stand on its own on a page, in a document, or on a website. It is usually set on related content items such as comments, forum posts, newspaper articles or other items grouped together on one page. It can be added to generic elements like <div> to convey this role, for example:
<div role="article">
<h2>Heading</h2>
<p>Content...</p>
</div>Instead of using this role, it’s preferrable to use the native <article> element like this:
<article>
<h2>Heading</h2>
<p>Content...</p>
</article>The <header> HTML element represents introductory content, typically a group of introductory or navigational aids, and has an implicit role of banner, so specifying this role is redundant.
The following example represents a banner using the role attribute:
<div role="banner">
<img src="companylogo.svg" alt="my company name" />
<h1>Title</h1>
<p>Subtitle</p>
</div>By default, the HTML5 <header> element has an identical meaning to the banner landmark, unless it is a descendant of <aside>, <article>, <main>, <nav>, or <section>, at which point <header> is the heading for that section and not the equivalent of the site-wide banner.
This example uses the <header> element instead of the banner role:
<header>
<img src="companylogo.svg" alt="my company name" />
<h1>Title</h1>
<p>Subtitle</p>
</header>The <big> tag is now obsolete. It was used to increase the size of text, you can do that using CSS instead. For example:
<p>Now this is <span style="font-size: larger;">big</span></p><img> tags no longer accept a border attribute. This can be defined using CSS instead, for example:
<img src="..." alt="..." style="border:0;" />The button role is used to make an element appear as a button control to a screen reader and can be applied to otherwise non-interactive elements like <div>. If you’re already using a <button> element, then it’s redundant to apply it the role button, as that’s implicit.
<!-- Instead of this -->
<button role="button">Buy</button>
<!-- Do this -->
<button>Buy</button>The button role is used to make an element appear as a button control to a screen reader and can be applied to otherwise non-interactive elements like <div>. If you’re already using an <input> element whose type is submit, then it’s redundant to apply it the role button, as that’s implicit.
<!-- Instead of this -->
<input type="submit" role="button">Buy</button>
<!-- Do this -->
<input type="submit">Buy</button>The <summary> HTML element specifies a clickable summary, caption, or legend for a <details> element’s disclosure box. As the <summary> element has an implicit button role, it’s not needed to include it explicitly.
Here’s an example, clicking the <summary> element toggles the state of the parent <details> element open and closed.
<details>
<summary>I have keys but no doors. I have space but no room. You can enter but can’t leave. What am I?</summary>
A keyboard.
</details>The <center> tag is no longer valid in HTML, you should use CSS instead, for example:
<p style="text-align:center">this text will be centered</p>