Default[f] gives the default value for arguments of the function f obtained with a _. pattern object. Default[f, i] gives the default value to use when _. appears as the ...

DeleteContents is an option for DeleteDirectory that specifies whether the contents of directories should automatically be deleted.

DelimiterFlashTime is an option for cells and notebooks that specifies how long in seconds a delimiter should flash when its matching delimiter is entered.

Deployed is an option for displayed objects, cells, and notebooks that specifies whether their contents should be considered deployed, so that elements such as Slider, ...

DiacriticalPositioning is an option for UnderscriptBox and related boxes that specifies how close diacritical characters are drawn to the base character.

Direction is an option for Limit that specifies the direction in which the limit is taken.

Editable is an option for displayed objects, cells, and notebooks that specifies whether their contents can be edited interactively using the front end.

EllipticExpPrime[u, {a, b}] gives the derivative of EllipticExp[u, {a, b}] with respect to u.

Evaluatable is an option for Cell that specifies whether a cell should be used as input to be evaluated by the Mathematica kernel.

Evaluator is an option for objects such as Button, Dynamic, and Cell that gives the name of the kernel to use to evaluate their contents.