回答:
man zshall /forward-word /backward-word
echo $WORDCHARS
*?_-.[]~=/&;!#$%^(){}<>
WORDCHARS='*?_-.[]~=&;!#$%^(){}<>' ;# without /
WORDCHARS=${WORDCHARS//[\/]}です。
WORDCHARS=${WORDCHARS/\/}
WORDCHARS=$WORDCHARS:s:/: