HTML Guides for selected

In HTML, boolean attributes like selected work differently than you might expect if you’re coming from a programming language. A boolean attribute’s presence alone means “true,” and its absence means “false.” Setting selected="true" is invalid because the only permitted values for a boolean attribute are the empty string ("") or the attribute’s own name (e.g., selected="selected"). The value "true" is not recognized by the HTML specification, which is why the W3C validator flags it.

This matters for several reasons. First, it violates the WHATWG HTML specification, which explicitly defines how boolean attributes must be written. Second, while most browsers are forgiving and will still treat selected="true" as if the option is selected, relying on this lenient behavior is risky — it can lead to inconsistencies across browsers or tools that parse HTML strictly. Third, invalid markup can cause problems for assistive technologies, automated testing tools, and server-side HTML processors that follow the spec closely.

The same rule applies to other boolean attributes like disabled, checked, readonly, multiple, required, and hidden. None of them should be set to "true" or "false".

It’s also worth noting that setting a boolean attribute to "false" (e.g., selected="false") does not turn it off — the attribute’s mere presence activates it. To deactivate a boolean attribute, you must remove it entirely from the element.

Examples

❌ Invalid: using selected="true"

<select name="color">
  <option selected="true">Red</option>
  <option>Green</option>
  <option>Blue</option>
</select>

This triggers the validation error because "true" is not a valid value for the boolean selected attribute.

✅ Valid: bare attribute (preferred)

<select name="color">
  <option selected>Red</option>
  <option>Green</option>
  <option>Blue</option>
</select>

The simplest and most common way to write a boolean attribute — just include the attribute name with no value.

✅ Valid: empty string value

<select name="color">
  <option selected="">Red</option>
  <option>Green</option>
  <option>Blue</option>
</select>

An empty string is a valid value for any boolean attribute per the HTML spec.

✅ Valid: attribute name as value

<select name="color">
  <option selected="selected">Red</option>
  <option>Green</option>
  <option>Blue</option>
</select>

Using the attribute’s own name as its value is also valid. This form is sometimes seen in XHTML-style markup and in templating systems.

❌ Invalid: using selected="false" to deselect

<select name="color">
  <option selected="false">Red</option>
  <option>Green</option>
  <option>Blue</option>
</select>

This is both invalid and misleading. The option will still be selected because the selected attribute is present. To not select an option, simply omit the attribute:

<select name="color">
  <option>Red</option>
  <option>Green</option>
  <option>Blue</option>
</select>