attribute reference
Expression[<name>[=<value>]]
Attribute references are similar to CSS attribute references, and may or may not include a value.
<button _="on click add @disabled">Disable Me!</button>
<button _="on click remove [@disabled]">Enable Me!</button>
<button type="button" _="on click add [@type='submit']">Change My Type!</button>
<button type="button" _="on click my @type to 'submit'">Change My Type As Well!</button>