HTML Checking for Large Sites

The <table> element does not accept a height attribute. Use CSS instead.

A CSS definition for background-image could not be understood by the parser. Check its definition to ensure that it’s well formed and that it contains an appropriate value.

The value on the display property is not valid.

The display CSS property sets whether an element is treated as a block or inline element and the layout used for its children, such as flow layout, grid or flex.

Learn more:

• MDN: CSS display property

The specified CSS filter is not a standard one, and may only work in some browsers.

Check out the Filter Effects W3C Working Draft

font-display isn’t a CSS property, it’s a descriptor for use with the @font-face at-rule.

Learn more:

• Can I Use… font-display
• MDN: font-display
• MDN: At-rules
• W3C Validator issue on font-display

The value specified for the min-height CSS attribute is not valid.

Learn more:

• MDN: CSS min-height

An invalid CSS property is being used. Properties starting with mso- are commonly defined by Microsoft products like Office and Outlook.

These properties, like mso-spacerun, mso-fareast-font-family, mso-bidi-font-weight, mso-margin-bottom-alt, mso-margin-top-alt and others starting with mso- are not standard CSS properties.

Padding properties, unline margin properties, don’t accept negative values. Read more about the CSS box model

The value break-word for the property word-break is deprecated, you should replace it with a valid value.

According to the CSS Text Module Level 3 spec:

For compatibility with legacy content, the word-break property also supports a deprecated break-word keyword. When specified, this has the same effect as word-break: normal and overflow-wrap: anywhere, regardless of the actual value of the overflow-wrap property.

Learn more:

• MDN: word-break
• CSS Text Module Level 3: word-break property
• W3C Validator issue on break-word

The ::file-selector-button has not been recognized by the W3C Validator. This seems to be a bug in the W3C Validator, which has already been reported.

Learn more:

• MDN: file-selector-button
• MDN: pseudo elements
• W3C: file-selector pseudo element

CSS can’t be properly processed because a computed style is missing a value it depends on.

A CSS definition for an X property could not be understood by the parser. Check it to ensure that it’s well formed and that it contains an appropriate value.

The specified CSS property is not valid.

Learn more:

• Can I Use…

<td> elements no longer accept an align attribute. This can be achieved using CSS like this:

<td style="text-align:center;">content</td>

<img> tags no longer accept a border attribute. This can be defined using CSS instead, for example:

<img src="..." alt="..." style="border:0;" />

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>

The <font> element, used to define the font face, size and color in previous versions of HTML, is no longer valid in HTML5. Instead, you should rely on CSS styles.

For example, you can define a font size of 12px, bold text with inline styles like this:

<p style="font-size: 12px; font-weight: bold;">some text</p>

Learn more about CSS fonts:

• MDN: CSS font

The <tt> tag, used in HTML4 to apply a monospaced (fixed width) font to the text, was deprecated in HTML5. Instead, you should use CSS to apply the desired font.

Example, instead of this deprecated code:

<tt>This is deprecated</tt>

You can define a monospaced text using font-family:

<span style="font-family: monospace;">This is monospaced text</span>

Learn more:

• MDN: font-family

The HTML <style> element contains style information for a document, or part of a document, defined in CSS. This element does not need the type attribute anymore, so it should be omitted.

For example, this style defines that <p> elements should be in red color.

<style type="text/css">
p {
  color: red;
}
</style>
<p>This text will be red.</p>

But, the type attribute is not used anymore, so we can just use this:

<style>
p {
  color: red;
}
</style>
<p>This text will be red.</p>

Read more:

• MDN: The Style information element
• WordPress plugin: Type Attribute Warnings Removal

<td> elements no longer accept a valign attribute. This can be achieved using CSS like this:

<td style="vertical-align:middle;">content</td>

Both <table> and <td> elements no longer accept a width attribute. Instead, you should use CSS as in this example:

<table style="width:100%;">
  <tr>
    <td style="width:50px;">Name</td>
  </tr>
</table>

You’re using an attribute X that is no longer valid for element Y, but you can use CSS to achieve the same effect.