Android layout style differences

Android layout style differences

I am trying to understand the difference between the above 2 styles. It
appears after reading various posts the correct way of doing this is
assigning the holo theme in the manifest and then doing
style="?android:attr/borderlessButtonStyle"
but it appears you can also do this
style="@android:style/Widget.Holo.Light.Button.Borderless.Small"
which one is correct? Is one an alias for the other?
I must admit the second 1 seems easier to read and understand, its
pointing to an internal style - right?
and the 1st one? this is a style or just an attribute within a style?
In the 1st one it also starts with a question mark, what purpose does this
have ?
anybody have a good insight into this ?