If maxsplit is given, at most maxsplit splits are done
(thus, the character vector will have at most maxsplit + 1 elements).
If maxsplit is not specified, then there is no limit on the number of
splits (all possible splits are made). If sep is given, consecutive
delimiters are not grouped together and are deemed to delimit empty strings.
The sep argument may consist of multiple characters. If sep is
not specified, any whitespace string is a separator. Splitting an empty
string returns an empty string.