Boolean attribute (HTML)

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A boolean attribute in {{Glossary("HTML")}}  is an {{glossary("attribute")}}  that represents true or false values. If an HTML tag contains a boolean attribute — no matter the value of that attribute — the attribute is set to true on that element. If an HTML tag does not contain the attribute, the attribute is set to false.

If the attribute is present, it can have one of the following forms:

• the attribute name alone; e.g., attribute, meaning its implicit value is the empty string
• the attribute with a value of the empty string; e.g., attribute=""
• the attribute with a value of the attribute’s name itself, with no leading or trailing whitespace and case ignored; e.g., attribute="attribute", attribute="ATTRIBUTE"

[!NOTE] The strings “true” and “false” are invalid values. To set the attribute to false, the attribute should be omitted altogether. Though modern browsers treat any string value as true, you should not rely on that behavior.

Here’s an example of a HTML boolean attribute checked:

<!-- The following checkboxes will be checked on initial rendering -->
<input type="checkbox" checked />
<input type="checkbox" checked="" />
<input type="checkbox" checked="checked" />
<input type="checkbox" checked="Checked" />

<!-- The following checkbox will not be checked on initial rendering -->
<input type="checkbox" />

See also

• Boolean attributes
• Boolean attributes in HTML specification
• Related glossary terms:
  • {{Glossary("Attribute")}} 
  • {{Glossary("Enumerated", "Enumerated attribute")}}