word-combining-categories

word-combining-categories is a variable defined in `C source code'.
Its value is

((nil . 94) (94) (67 . 72) (67 . 75))

Documentation:
List of pair (cons) of categories to determine word boundary.

Emacs treats a sequence of word constituent characters as a single
word (i.e. finds no word boundary between them) only if they belong to
the same script. But, exceptions are allowed in the following cases.

(1) The case that characters are in different scripts is controlled
by the variable `word-combining-categories'.

Emacs finds no word boundary between characters of different scripts
if they have categories matching some element of this list.

More precisely, if an element of this list is a cons of category CAT1
and CAT2, and a multibyte character C1 which has CAT1 is followed by
C2 which has CAT2, there's no word boundary between C1 and C2.

For instance, to tell that Han characters followed by Hiragana
characters can form a single word, the element `(?C . ?H)' should be
in this list.

(2) The case that character are in the same script is controlled by
the variable `word-separating-categories'.

Emacs finds a word boundary between characters of the same script
if they have categories matching some element of this list.

More precisely, if an element of this list is a cons of category CAT1
and CAT2, and a multibyte character C1 which has CAT1 but not CAT2 is
followed by C2 which has CAT2 but not CAT1, there's a word boundary
between C1 and C2.

For instance, to tell that there's a word boundary between Hiragana
and Katakana (both are in the same script `kana'),
the element `(?H . ?K) should be in this list.