A melhor maneira é zshall (1), que contém documentação sobre esses e todos os recursos do zsh, e é facilmente pesquisável no seu pager favorito (menos é mais):
$ man zshall
zsh -x -o shwordsplit scr
runs the script scr, setting the XTRACE option by the
corresponding letter '-x' and the SH_WORD_SPLIT option by name.
[…]
SH_WORD_SPLIT (-y) <K> <S>
Causes field splitting to be performed on unquoted parameter
expansions. Note that this option has nothing to do with word
splitting. (See the section 'Parameter Expansion'.)
e
The simplest way of configuring the functions is to use
select-word-style, which can either be called as a normal
function with the appropriate argument, or invoked as a
user-defined widget that will prompt for the first character of
the word style to be used. The first time it is invoked, the
eight -match functions will automatically replace the builtin
versions, so they do not need to be loaded explicitly.