NumberSeparator is an option for NumberForm and related functions which gives the string to insert at breaks between digits.
NumberSeparator -> "s" specifies that the string s should be inserted at every break between digits specified by DigitBlock.
NumberSeparator -> "sleft", "sright" specifies different strings to be used on the left and right of the decimal point.
The default setting is NumberSeparator -> ",".
See Section 2.9.7.
New in Version 1.