DefaultButton[] represents an OK button that closes a dialog, and is the default when DynamicBox[ToBoxes[If[$OperatingSystem === "MacOSX", "Return", "Enter"], StandardForm], ...
Defer
(Built-in Mathematica Symbol) Defer[expr] yields an object that displays as the unevaluated form of expr, but that is evaluated if it is explicitly given as Mathematica input.
DependentVariables is an option which specifies the list of all objects that should be considered as dependent variables in equations that have been supplied.
DynamicSetting[e] represents an object which displays as e, but is interpreted as the dynamically updated current value of Setting[e] if supplied as Mathematica ...
ExponentialGeneratingFunction[expr, n, x] gives the exponential generating function in x for the sequence whose n\[Null]^th term is given by the expression ...
Extract
(Built-in Mathematica Symbol) Extract[expr, list] extracts the part of expr at the position specified by list. Extract[expr, {list_1, list_2, ...}] extracts a list of parts of expr. Extract[expr, list, h] ...
FontProperties -> {opt_1 -> val_1, opt_2 -> val_2} specifies font properties.
FractionBox[x, y] is a low-level formatting construct that represents x/y in notebook expressions.
FractionBoxOptions -> {opt_1 -> val_1, opt_2 -> val_2, ...} is an option for cells that specifies settings for FractionBox objects within the cell.
FrontEndEventActions is an option for the notebook front end that gives a list of actions to perform when specified user-interface events occur.