Bad value “1” for attribute “selected” on element “option”.

The selected attribute on the <option> element is a boolean attribute and does not accept a value like "1".

Boolean attributes in HTML don't need a value at all. Their mere presence on an element means "true," and their absence means "false." When you write selected="1", the W3C validator flags it because "1" is not a valid value for a boolean attribute.

According to the HTML specification, a boolean attribute can only have three valid forms: the attribute name alone (selected), an empty string (selected=""), or the attribute's own name as the value (selected="selected"). Any other value, including "1", "true", or "yes", is invalid.

Invalid Example

<select name="color">
  <option value="red">Red</option>
  <option value="blue" selected="1">Blue</option>
  <option value="green">Green</option>
</select>

Valid Example

<select name="color">
  <option value="red">Red</option>
  <option value="blue" selected>Blue</option>
  <option value="green">Green</option>
</select>

Using just selected without a value is the cleanest and most common approach.

Learn more:

MDN Reference

HTML option element - MDN

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MDN Reference

HTML select element - MDN

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WHATWG Spec

WHATWG HTML Standard - Forms

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