4.14. Disabled elements
An element is said to be actually disabled if it falls into one of the following categories:
- a 
buttonelement that is disabled - an 
inputelement that is disabled - a 
selectelement that is disabled - a 
textareaelement that is disabled - an 
optgroupelement that has adisabledattribute - an 
optionelement that is disabled - a 
menuitemelement that has adisabledattribute - a 
fieldsetelement that is a disabled fieldset 
 This definition is used to determine what elements can be focused and which elements match the :disabled pseudo-class.