What is the difference between readonly=“true” & readonly=“readonly”?

Question

What is the difference between:

and:

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Answer 1

readonly="true" is invalid HTML5, readonly="readonly" is valid.

HTML5 spec:

http://www.w3.org/TR/html5/forms.html#attr-input-readonly :

The readonly attribute is a boolean attribute

http://www.w3.org/TR/html5/infrastructure.html#boolean-attributes :

The presence of a boolean attribute on an element represents the true value, and the absence of the attribute represents the false value.

If the attribute is present, its value must either be the empty string or a value that is an ASCII case-insensitive match for the attribute's canonical name, with no leading or trailing whitespace.

Conclusion:

The following are valid, equivalent and true:

The following are invalid:

The absence of the attribute is the only valid syntax for false:

Recommendation

If you care about writing valid XHTML, use readonly="readonly", since is invalid and other alternatives are less readable. Else, just use as it is shorter.