StyleDefinitions is an option for notebooks that gives definitions for the styles that can be used in a notebook.
SubscriptBox[x, y] is the low-level box representation for x_y in notebook expressions.
Subscript[x, y] is an object that formats as x_y. Subscript[x, y_1, y_2, ...] formats as x Subscript[y, 1], Subscript[y, 2], ....
x -= dx subtracts dx from x and returns the new value of x.
x - y is equivalent to x + (-1*y).
SuperscriptBox[x, y] is the low-level box representation for x^y in notebook expressions.
Switch
(Built-in Mathematica Symbol) Switch[expr, form_1, value_1, form_2, value_2, ...] evaluates expr, then compares it with each of the form_i in turn, evaluating and returning the value_i corresponding to ...
SymbolName[symbol] gives the name of the specified symbol.
SynchronousUpdating is an option for Manipulate, Dynamic, and related functions that specifies whether or not to evaluate their contents synchronously.
SyntaxForm is an option for InterpretationBox and TagBox objects that specifies the precedence level to use when the InterpretationBox or TagBox is considered as an operator.