SubscriptBox[x, y] represents in input and output.
Inside \( ... \) SubscriptBox[x, y] can be input as x \_ y.
In a notebook a SubscriptBox can be created using - or _. moves out of the subscript.
In StandardForm and InputForm, SubscriptBox[x, y] is interpreted on input as Subscript[x, y].
The baseline of SubscriptBox[x, y] is taken to be the baseline of x.
SubscriptBox[x, y] is usually output with y in a smaller font than x.
In StandardForm, explicit SubscriptBox objects are output literally. You can use DisplayForm to see the display form of such objects.
See Section 2.9.10.
See also: SuperscriptBox, SubsuperscriptBox, UnderscriptBox, ScriptSizeMultipliers.
New in Version 3.