The MatchFence procedure locates the matching fence character to one specified in the input text s by its position pos. It returns the position, in s, of the matching fence character if present, or $0$ otherwise. If $s_{\mathrm{pos}}$ is not a fence character, that is, not one of $\left\{''(''\,'')''\,''[''\,'']''\,''\{''\,''\}''\right\}$, an exception is raised.

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.

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

$\mathrm{MatchFence}\left(''ab\{cde\}fg''\,3\right)$

$7$

$n≔\mathrm{MatchFence}\left(''ab(cde)fg''\,3\right)$

$n≔7$

$\mathrm{MatchFence}\left(''ab(cde)fg''\,n\right)$

$3$

$\mathrm{MatchFence}\left(''ab(cde)fg''\,1\right)$

Error, (in StringTools:-MatchFence) the character `a' is not a fence character

$\mathrm{MatchFence}\left(''ab[cdefg''\,3\right)$

$0$

$\mathrm{MatchFence}\left(''ab\{cde]fg''\,3\right)$

$0$