The MaximalPalindromicSubstring command  computes a maximal palindromic substring of the string s. A string $t$ is a palindrome if it is equal to itself reversed, that is, $t=\mathrm{Reverse}\left(t\right)$.

If s is nonempty and contains no substrings that are palindromes, the first character of s is the maximal palindromic substring. If s is empty, the empty string ("") is the maximal palindromic substring.

The maximal palindromic substring of s is indicated by returning a sequence of two non-negative integers:

The first is the index of the beginning of the palindromic substring in the string s.

The second is the length of the palindromic substring.

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.

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

$\mathrm{MaximalPalindromicSubstring}\left(''''\right)$

$0,0$

$\mathrm{MaximalPalindromicSubstring}\left(''abcde''\right)$

$1,1$

$\mathrm{pos},\mathrm{len}≔\mathrm{MaximalPalindromicSubstring}\left(''abcbde''\right)$

$\mathrm{pos},\mathrm{len}≔2,3$

$''abcbde''\left[\mathrm{pos}..\mathrm{pos}+\mathrm{len}-1\right]$

$''bcb''$