The Insert(s, position, t) command inserts a string t into the string s at position. The value of position must be an integer in the range $0..\mathrm{length}\left(s\right)$. Position $0$ is the position before the first character of s; position $1$ is the position after the first character of s; position $2$ is the position after the second character of s; and so on. Thus, Insert( s, 0, t ) is equivalent to $\mathrm{cat}\left(t\,s\right)$, while Insert( s, length( s ), t ) is equivalent to $\mathrm{cat}\left(s\,t\right)$.

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.

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

$\mathrm{Insert}\left(''abcd''\,0\,''=''\right)$

$''=abcd''$

$\mathrm{Insert}\left(''abcd''\,1\,''=''\right)$

$''a=bcd''$

$\mathrm{Insert}\left(''abcd''\,2\,''=''\right)$

$''ab=cd''$

$\mathrm{Insert}\left(''abcd''\,3\,''=''\right)$

$''abc=d''$

$\mathrm{Insert}\left(''abcd''\,4\,''=''\right)$

$''abcd=''$

$\mathrm{Insert}\left(''abcd''\,5\,''=''\right)$

Error, (in StringTools:-Insert) string index `5' out of range

$\mathrm{Insert}\left(''''\,0\,''Foo''\right)$

$''Foo''$

$\left\{\mathrm{seq}\right\}\left(\mathrm{Insert}\left(''abc''\,n\,''''\right)\,n=0..\mathrm{length}\left(''abc''\right)\right)$

$\left\{''abc''\right\}$