The WordStart command returns the index of the beginning (first letter) of the word containing the index index, if any. If the second argument index does not occur in a word in the string s, then the value $0$ is returned.

The WordEnd command returns the index of the end (last letter) of the word containing the index index, if any. If the second argument index does not occur in a word in the string s, then the value $0$ is returned.

The WordContaining command returns the word containing the index index, if index lies within a word in the string s, or the empty string $''''$, otherwise.

For all three commands, the second argument index must be a valid index into the string presented as the first argument.

If the index index lies within a word in the string s, then WordContaining( s, index ) = s[ WordStart( s, index ) .. WordEnd( s, index ) ].

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.

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

$\mathrm{WordStart}\left(''Voi\; che\; sapete,\; che\; cosa\; e\; amor,\; donne,\; vedete,\; s\text{'}io\; l\text{'}ho\; nel\; cor.''\,7\right)$

$5$

$\mathrm{WordEnd}\left(''Voi\; che\; sapete,\; che\; cosa\; e\; amor,\; donne,\; vedete,\; s\text{'}io\; l\text{'}ho\; nel\; cor.''\,7\right)$

$7$

$\mathrm{WordContaining}\left(''Voi\; che\; sapete,\; che\; cosa\; e\; amor,\; donne,\; vedete,\; s\text{'}io\; l\text{'}ho\; nel\; cor.''\,7\right)$

$''che''$