a generalized boolean.

implementation-dependent.

Controls the format in which arrays are printed. If it is false, the contents of arrays other than strings are never printed. Instead, arrays are printed in a concise form using #< that gives enough information for the user to be able to identify the array, but does not include the entire array contents. If it is true, non-string arrays are printed using #(...), #*, or #nA syntax.

The implementation.

Section 2.4.8.3 (Sharpsign Left-Parenthesis), Section 2.4.8.20 (Sharpsign Less-Than-Sign)