Categories provide an alternate way of classifying characters syntactically. You can define several categories as needed, then independently assign each character to one or more categories. Unlike syntax classes, categories are not mutually exclusive; it is normal for one character to belong to several categories.
Each buffer has a category table which records which categories are defined and also which characters belong to each category. Each category table defines its own categories, but normally these are initialized by copying from the standard categories table, so that the standard categories are available in all modes.
Each category has a name, which is an ASCII printing character in
the range ‘ ’ to ‘~’. You specify the name of a category
when you define it with
The category table is actually a char-table (see Char-Tables). The element of the category table at index c is a category set—a bool-vector—that indicates which categories character c belongs to. In this category set, if the element at index cat is t, that means category cat is a member of the set, and that character c belongs to category cat.
For the next three functions, the optional argument table defaults to the current buffer’s category table.
define-categorychar docstring &optional table
This function defines a new category, with name char and documentation docstring, for the category table table.
Here’s an example of defining a new category for characters that have strong right-to-left directionality (see Bidirectional Display) and using it in a special category table. To obtain the information about the directionality of characters, the example code uses the ‘bidi-class’ Unicode property (see bidi-class).
(defvar special-category-table-for-bidi ;; Make an empty category-table. (let ((category-table (make-category-table)) ;; Create a char-table which gives the 'bidi-class' Unicode ;; property for each character. (uniprop-table (unicode-property-table-internal 'bidi-class))) (define-category ?R "Characters of bidi-class R, AL, or RLO" category-table) ;; Modify the category entry of each character whose 'bidi-class' ;; Unicode property is R, AL, or RLO -- these have a ;; right-to-left directionality. (map-char-table #'(lambda (key val) (if (memq val '(R AL RLO)) (modify-category-entry key ?R category-table))) uniprop-table) category-table))
category-docstringcategory &optional table
This function returns the documentation string of category category in category table table.
(category-docstring ?a) ⇒ "ASCII" (category-docstring ?l) ⇒ "Latin"
This function returns a category name (a character) which is not
currently defined in table. If all possible categories are in use
in table, it returns
This function returns the current buffer’s category table.
This function returns t if object is a category table,
This function returns the standard category table.
This function constructs a copy of table and returns it. If
table is not supplied (or is
nil), it returns a copy of the
standard category table. Otherwise, an error is signaled if table
is not a category table.
This function makes table the category table for the current buffer. It returns table.
This creates and returns an empty category table. In an empty category table, no categories have been allocated, and no characters belong to any categories.
This function returns a new category set—a bool-vector—whose initial
contents are the categories listed in the string categories. The
elements of categories should be category names; the new category
set has t for each of those categories, and
nil for all
(make-category-set "al") ⇒ #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0"
This function returns the category set for character char in the
current buffer’s category table. This is the bool-vector which
records which categories the character char belongs to. The
char-category-set does not allocate storage, because
it returns the same bool-vector that exists in the category table.
(char-category-set ?a) ⇒ #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0"
This function converts the category set category-set into a string containing the characters that designate the categories that are members of the set.
(category-set-mnemonics (char-category-set ?a)) ⇒ "al"
modify-category-entrychar category &optional table reset
This function modifies the category set of char in category
table table (which defaults to the current buffer’s category
table). char can be a character, or a cons cell of the form
(min . max); in the latter case, the function
modifies the category sets of all characters in the range between
min and max, inclusive.
Normally, it modifies a category set by adding category to it.
But if reset is non-
nil, then it deletes category
This function describes the category specifications in the current
category table. It inserts the descriptions in a buffer, and then
displays that buffer. If buffer-or-name is non-
describes the category table of that buffer instead.