23
2010
Indeterminate Radio Buttons
There is a pseudo class selector, :indeterminate, whose job it can be to select radio button inputs which are neither selected (have attribute “checked”) or unselected (don’t have that). This is a CSS3 selector, which may be in response to the HTML5 spec, which explicitly allows radio buttons to be in this state:
read more...If none of the radio buttons in a radio button group are checked when they are inserted into the document, then they will all be initially unchecked in the interface, until such time as one of them is checked (either by the user or by script).

