The IsSorted(s) command tests whether the characters in the string s appear in sorted order.

If s is the empty string, the command returns true.

All of the StringTools package commands treat strings as (null-terminated) sequences of $8$-bit (ASCII) characters.  Thus, there is no support for multibyte character encodings, such as unicode encodings.

$\mathrm{with}\left(\mathrm{StringTools}\right)\:$

$\mathrm{IsSorted}\left(''abc''\right)$

$\mathrm{true}$

$\mathrm{IsSorted}\left(''acb''\right)$

$\mathrm{false}$

$\mathrm{IsSorted}\left(''aabbcdee''\right)$

$\mathrm{true}$

$\mathrm{IsSorted}\left(\mathrm{Sort}\left(\mathrm{Random}\left(1000000\,'\mathrm{lower}'\right)\right)\right)$

$\mathrm{true}$