As approved in #4721 (comment), and later amended in #5125 (comment):

After the enhancement, only a <Max-substrings> value of 0 will be accepted as the explicit signal that all tokens should be returned, however many are found in the input string(s).

Negative <Max-substrings> values will work analogously to the already supported positive values, except that:

• they return the specified number of strings from the end of the string(s).

• all individually extracted tokens are returned in input order, and whatever unsplit part remains, if any, is returned as the first token.

Examples:

PS> 'a b c d' -split ' ', -2  # split into (at most) 2 strings from the end
a b c  # prefix
d        # requested token

PS> 'a b c d' -split ' ', -3  # split into (at most) 3 strings from the end
a b   # prefix
c       
d 

PS> 'a b' -split ' ', -2  # 2 resulting strings - complete split; same as 0 in this case
a
b

Note that both -split ' ', 1 and -split ' ', -1 are no-ops: they request no splitting at all, and the sign of the <Max-substrings> argument is therefore irrelevant.

Reporting the prefix (unsplit part) first enables the following idiom:

PS> $prefix, $tokens = 'a b c d' -split ' ', -3 # -> $prefix = 'a b', $tokens = 'c', 'd'

Environment data

PowerShell Core v6.0.0-beta.8