I had a surprising amount of difficulty finding a complete list of HTML attributes that don’t require values, so I decided to make a reference list. Note that these attributes simply have a default value of some sort; not all of them are boolean. Also, all these attributes require values in XHTML.
Here’s an example of how you might use the checked attribute in HTML5:
And in XHTML:
That’s basically how they all work, except a few attributes have camel-cased values for some reason. I’m not documenting those here, though.
The following list was taken from this github issue (thanks to these folk for their hard work). I’ve tweaked it a bit and matched the attributes to their relevant HTML tags/context. Let me know if I’ve missed anything!