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] ...
FrontEndEventActions is an option for the notebook front end that gives a list of actions to perform when specified user-interface events occur.
HoldForm[expr] prints as the expression expr, with expr maintained in an unevaluated form.
ScheduledTaskObject[id, expr, spec, ...] is a task object specifying future evaluation of expr according to spec.
Slider2D[{x, y}] represents a 2D slider with settings x and y in the range 0 to 1. Slider2D[Dynamic[pt]] takes the setting to be the dynamically updated current value of pt, ...
StartScheduledTask[obj] starts the task represented by obj.
Unevaluated[expr] represents the unevaluated form of expr when it appears as the argument to a function.
ViewVertical is an option for Graphics3D and related functions which specifies what direction in scaled coordinates should be vertical in the final image.
$MaxMachineNumber is the largest machine-precision number that can be used on a particular computer system.
$MaxPrecision gives the maximum number of digits of precision to be allowed in arbitrary-precision numbers.