[javascript] input checkbox true or checked or yes

I've seen the three implementations of pre-selecting a checkbox. I started off using checked="checked" because I thought it was the "proper" way (never did like the "checked"="yes" however). I am thinking of changing to checked="true" as it seems more readable and is easier to code the JavaScript. Note that this same question applies to other attributes such as "disabled"="disabled" versus "disabled"="true". As long as I am consistent, is using "true" the preferred approach? Thank you

<input type="checkbox" checked="checked" value="123" name="howdy" />
<input type="checkbox" checked="true"    value="123" name="howdy" />
<input type="checkbox" checked="yes"     value="123" name="howdy" />

Accordingly to W3C checked input's attribute can be absent/ommited or have "checked" as its value. This does not invalidate other values because there's no restriction to the browser implementation to allow values like "true", "on", "yes" and so on. To guarantee that you'll write a cross-browser checkbox/radio use checked="checked", as recommended by W3C.

disabled, readonly and ismap input's attributes go on the same way.

EDITED

empty is not a valid value for checked, disabled, readonly and ismap input's attributes, as warned by @Quentin