The Overlap(s,t) command computes the length of the overlap between s and t in linear time. This is defined to be the length of the longest suffix of s that is a prefix of t.

Note that, in general, Overlap( s, t ) and Overlap( t, s ) are different.

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.

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

$\mathrm{Overlap}\left(''abc''\,''def''\right)$

$0$

$\mathrm{Overlap}\left(''abc''\,''cdef''\right)$

$1$

$\mathrm{Overlap}\left(''abcdef''\,''defg''\right)$

$3$