InString[n] is a global object that is assigned to be the text of the n\[Null]^th input line.

x += dx adds dx to x and returns the new value of x.

ToRules[eqns] takes logical combinations of equations, in the form generated by Roots and Reduce, and converts them to lists of rules, of the form produced by Solve.

ListPlay[{a_1, a_2, ...}] creates an object that plays as a sound whose amplitude is given by the sequence of levels a_i.

PrependTo[s, elem] prepends elem to the value of s, and resets s to the result.

ToBoxes[expr] generates boxes corresponding to the printed form of expr in StandardForm. ToBoxes[expr, form] gives the boxes corresponding to output in the specified form.

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

ToString[expr] gives a string corresponding to the printed form of expr in OutputForm. ToString[expr, form] gives the string corresponding to output in the specified form.

ImageSizeMultipliers is an option that specifies how much smaller to render graphics that appear within other constructs.

CellBaseline is an option for Cell which specifies where the baseline of the cell should be assumed to be when it appears inside another cell.