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(elisp)Categories

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Categories
==========

   "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 `define-category'.

   The category table is actually a char-table (Note: 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.

 - Function: define-category char docstring &optional table
     This function defines a new category, with name CHAR and
     documentation DOCSTRING.

     The new category is defined for category table TABLE, which
     defaults to the current buffer's category table.

 - Function: category-docstring category &optional table
     This function returns the documentation string of category CATEGORY
     in category table TABLE.

          (category-docstring ?a)
               => "ASCII"
          (category-docstring ?l)
               => "Latin"

 - Function: get-unused-category table
     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 `nil'.

 - Function: category-table
     This function returns the current buffer's category table.

 - Function: category-table-p object
     This function returns `t' if OBJECT is a category table, otherwise
     `nil'.

 - Function: standard-category-table
     This function returns the standard category table.

 - Function: copy-category-table &optional 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 current
     category table.  Otherwise, an error is signaled if TABLE is not a
     category table.

 - Function: set-category-table table
     This function makes TABLE the category table for the current
     buffer.  It returns TABLE.

 - Function: make-category-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.

 - Function: make-category-set 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 other categories.

          (make-category-set "al")
               => #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0"

 - Function: char-category-set char
     This function returns the category set for character CHAR.  This
     is the bool-vector which records which categories the character
     CHAR belongs to.  The function `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"

 - Function: category-set-mnemonics category-set
     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"

 - Function: modify-category-entry character category &optional table
          reset
     This function modifies the category set of CHARACTER in category
     table TABLE (which defaults to the current buffer's category
     table).

     Normally, it modifies the category set by adding CATEGORY to it.
     But if RESET is non-`nil', then it deletes CATEGORY instead.

 - Command: describe-categories
     This function describes the category specifications in the current
     category table.  The descriptions are inserted in a buffer, which
     is then displayed.