Nu, nu cred ca este tratat diferit.

Attributes define desired behavior or indicate additional element properties. Most attributes require a value. In HTML, the value can be left unquoted if it doesn't include spaces (name=value), or it can be quoted with single or double quotes (name='value' or name="value"). In XML, those quotes are required. Boolean attributes, on the other hand, don't require a value to be specified.
sau http://mathiasbynens.be/notes/unquoted-attribute-values