Wolfram Language & System 11.0 (2016)|Legacy Documentation
creates a string by concatenating all the si, with spaces inserted between them.
creates a string by concatenating the sij, and inserting spaces at the lowest level and newlines at the higher level.
inserts the separator sep between all elements in list.
use left and right as delimiters after concatenation.
inserts separator sepi between elements of list at level i.