Required Properties with Default Values

For issue #787 this is a list of all required properties that have default values defined

Role	State/Property	Default Value
checkbox	aria-checked	false
combobox	aria-expanded	false
heading	aria-level	2
menuitemcheckbox	aria-checked	false
menuitemradio	aria-checked	false
option	aria-selected	false
radio	aria-checked	false
scrollbar	aria-orientation	vertical
scrollbar	aria-valuemin	0
scrollbar	aria-valuemax	100
scrollbar	aria-valuenow	halfway between valuemax and valuemin
separator (focusable)	aria-valuemin	0
separator (focusable)	aria-valuemax	100
separator (focusable)	aria-valuenow	50
slider	aria-valuemin	0
slider	aria-valuemax	100
slider	aria-valuenow	halfway between valuemax and valuemin
spinbutton	aria-valuemin	no minimum value
spinbutton	aria-valuemax	no maximum value
spinbutton	aria-valuenow	0
switch	aria-checked	false