AbsoluteOptions[expr] gives the absolute settings of options specified in an expression such as a graphics object. AbsoluteOptions[expr, name] gives the absolute setting for ...

AbsoluteTiming[expr] evaluates expr, returning a list of the absolute number of seconds in real time that have elapsed, together with the result obtained.

AllowGroupClose is an option for Cell that specifies whether a cell group can be closed normally.

AllowReverseGroupClose is an option for Cell that specifies whether a cell group can be reverse closed.

Array[f, n] generates a list of length n, with elements f[i]. Array[f, {n_1, n_2, ...}] generates an n_1*n_2*... array of nested lists, with elements f[i_1, i_2, ...]. ...

AtomQ[expr] yields True if expr is an expression which cannot be divided into subexpressions, and yields False otherwise.

AutoMultiplicationSymbol is an option for objects such as Cell and Notebook that specifies whether to automatically display a multiplication symbol between numbers that would ...

BitNot[n] gives the bitwise NOT of the integer n.

BitShiftRight[n, k] shifts the binary bits in the integer n to the right by k places, dropping bits that are shifted past the unit's position on the right. BitShiftRight[n] ...

_or Blank[] is a pattern object that can stand for any Mathematica expression. _h or Blank[h] can stand for any expression with head h.