This is documentation for Mathematica 4, which was
based on an earlier version of the Wolfram Language.

PadLeft[list, n] makes a list of length n by padding list with zeros on the left.

PadLeft[list, n, , , ... ] pads by cyclically repeating the elements .

PadLeft[list, , , ... ] makes a nested list with length at level i.

PadLeft[list, n, ... ] always returns a list of length n, except in some special cases where padding is {}.

With padding , , ... , cyclic repetitions of the are effectively laid down and then the list is superimposed on top of them, with the last element of the list lying on an occurrence of .

A margin of Round[(n-Length[list])/2] effectively centers list.

PadLeft[list, n, list] effectively treats list as cyclic.

PadLeft[list, n, xlist] can be used to repeat an individual element that is itself a list.

PadLeft[, n, , , ... ] repeats the sequence of as many times as fits in a list of length n.

PadLeft[list, , , ... ] creates a full array with dimensions , , ... even if list is ragged.

Negative specify to pad on the right.

PadLeft[list, , , , , ... , , ... , ... ] pads by repeating the block of .

PadLeft[list, , , ... , list] effectively treats list as cyclic in every dimension.

PadLeft[list, , , ... , padding, , , ... ] uses margin at level i.

The object list need not have head List.

See The Mathematica Book: Section 1.8.6.