+File: xemacs.info, Node: Disabling, Prev: Rebinding, Up: Key Bindings
+
+Disabling Commands
+------------------
+
+ Disabling a command marks it as requiring confirmation before it can
+be executed. The purpose of disabling a command is to prevent
+beginning users from executing it by accident and being confused.
+
+ The direct mechanism for disabling a command is to have a non-`nil'
+`disabled' property on the Lisp symbol for the command. These
+properties are normally set by the user's `.emacs' file with Lisp
+expressions such as:
+
+ (put 'delete-region 'disabled t)
+
+ If the value of the `disabled' property is a string, that string is
+included in the message printed when the command is used:
+
+ (put 'delete-region 'disabled
+ "Text deleted this way cannot be yanked back!\n")
+
+ You can disable a command either by editing the `.emacs' file
+directly or with the command `M-x disable-command', which edits the
+`.emacs' file for you. *Note Init File::.
+
+ When you attempt to invoke a disabled command interactively in Emacs,
+a window is displayed containing the command's name, its documentation,
+and some instructions on what to do next; then Emacs asks for input
+saying whether to execute the command as requested, enable it and
+execute, or cancel it. If you decide to enable the command, you are
+asked whether to do this permanently or just for the current session.
+Enabling permanently works by automatically editing your `.emacs' file.
+You can use `M-x enable-command' at any time to enable any command
+permanently.
+
+ Whether a command is disabled is independent of what key is used to
+invoke it; it also applies if the command is invoked using `M-x'.
+Disabling a command has no effect on calling it as a function from Lisp
+programs.
+
+\1f
+File: xemacs.info, Node: Syntax, Next: Init File, Prev: Key Bindings, Up: Customization
+
+The Syntax Table
+================
+
+ All the Emacs commands which parse words or balance parentheses are
+controlled by the "syntax table". The syntax table specifies which
+characters are opening delimiters, which are parts of words, which are
+string quotes, and so on. Actually, each major mode has its own syntax
+table (though sometimes related major modes use the same one) which it
+installs in each buffer that uses that major mode. The syntax table
+installed in the current buffer is the one that all commands use, so we
+call it "the" syntax table. A syntax table is a Lisp object, a vector
+of length 256 whose elements are numbers.
+
+* Menu:
+
+* Entry: Syntax Entry. What the syntax table records for each character.
+* Change: Syntax Change. How to change the information.
+
+\1f
+File: xemacs.info, Node: Syntax Entry, Next: Syntax Change, Up: Syntax
+
+Information About Each Character
+--------------------------------
+
+ The syntax table entry for a character is a number that encodes six
+pieces of information:
+
+ * The syntactic class of the character, represented as a small
+ integer
+
+ * The matching delimiter, for delimiter characters only (the
+ matching delimiter of `(' is `)', and vice versa)
+
+ * A flag saying whether the character is the first character of a
+ two-character comment starting sequence
+
+ * A flag saying whether the character is the second character of a
+ two-character comment starting sequence
+
+ * A flag saying whether the character is the first character of a
+ two-character comment ending sequence
+
+ * A flag saying whether the character is the second character of a
+ two-character comment ending sequence
+
+ The syntactic classes are stored internally as small integers, but
+are usually described to or by the user with characters. For example,
+`(' is used to specify the syntactic class of opening delimiters. Here
+is a table of syntactic classes, with the characters that specify them.
+
+` '
+ The class of whitespace characters.
+
+`w'
+ The class of word-constituent characters.
+
+`_'
+ The class of characters that are part of symbol names but not
+ words. This class is represented by `_' because the character `_'
+ has this class in both C and Lisp.
+
+`.'
+ The class of punctuation characters that do not fit into any other
+ special class.
+
+`('
+ The class of opening delimiters.
+
+`)'
+ The class of closing delimiters.
+
+`''
+ The class of expression-adhering characters. These characters are
+ part of a symbol if found within or adjacent to one, and are part
+ of a following expression if immediately preceding one, but are
+ like whitespace if surrounded by whitespace.
+
+`"'
+ The class of string-quote characters. They match each other in
+ pairs, and the characters within the pair all lose their syntactic
+ significance except for the `\' and `/' classes of escape
+ characters, which can be used to include a string-quote inside the
+ string.
+
+`$'
+ The class of self-matching delimiters. This is intended for TeX's
+ `$', which is used both to enter and leave math mode. Thus, a
+ pair of matching `$' characters surround each piece of math mode
+ TeX input. A pair of adjacent `$' characters act like a single
+ one for purposes of matching.
+
+`/'
+ The class of escape characters that always just deny the following
+ character its special syntactic significance. The character after
+ one of these escapes is always treated as alphabetic.
+
+`\'
+ The class of C-style escape characters. In practice, these are
+ treated just like `/'-class characters, because the extra
+ possibilities for C escapes (such as being followed by digits)
+ have no effect on where the containing expression ends.
+
+`<'
+ The class of comment-starting characters. Only single-character
+ comment starters (such as `;' in Lisp mode) are represented this
+ way.
+
+`>'
+ The class of comment-ending characters. Newline has this syntax in
+ Lisp mode.
+
+ The characters flagged as part of two-character comment delimiters
+can have other syntactic functions most of the time. For example, `/'
+and `*' in C code, when found separately, have nothing to do with
+comments. The comment-delimiter significance overrides when the pair of
+characters occur together in the proper order. Only the list and sexp
+commands use the syntax table to find comments; the commands
+specifically for comments have other variables that tell them where to
+find comments. Moreover, the list and sexp commands notice comments
+only if `parse-sexp-ignore-comments' is non-`nil'. This variable is set
+to `nil' in modes where comment-terminator sequences are liable to
+appear where there is no comment, for example, in Lisp mode where the
+comment terminator is a newline but not every newline ends a comment.
+
+\1f
+File: xemacs.info, Node: Syntax Change, Prev: Syntax Entry, Up: Syntax
+
+Altering Syntax Information
+---------------------------
+
+ It is possible to alter a character's syntax table entry by storing
+a new number in the appropriate element of the syntax table, but it
+would be hard to determine what number to use. Emacs therefore
+provides a command that allows you to specify the syntactic properties
+of a character in a convenient way.
+
+ `M-x modify-syntax-entry' is the command to change a character's
+syntax. It can be used interactively and is also used by major modes
+to initialize their own syntax tables. Its first argument is the
+character to change. The second argument is a string that specifies the
+new syntax. When called from Lisp code, there is a third, optional
+argument, which specifies the syntax table in which to make the change.
+If not supplied, or if this command is called interactively, the third
+argument defaults to the current buffer's syntax table.
+
+ 1. The first character in the string specifies the syntactic class.
+ It is one of the characters in the previous table (*note Syntax
+ Entry::).
+
+ 2. The second character is the matching delimiter. For a character
+ that is not an opening or closing delimiter, this should be a
+ space, and may be omitted if no following characters are needed.
+
+ 3. The remaining characters are flags. The flag characters allowed
+ are:
+
+ `1'
+ Flag this character as the first of a two-character comment
+ starting sequence.
+
+ `2'
+ Flag this character as the second of a two-character comment
+ starting sequence.
+
+ `3'
+ Flag this character as the first of a two-character comment
+ ending sequence.
+
+ `4'
+ Flag this character as the second of a two-character comment
+ ending sequence.
+
+ Use `C-h s' (`describe-syntax') to display a description of the
+contents of the current syntax table. The description of each
+character includes both the string you have to pass to
+`modify-syntax-entry' to set up that character's current syntax, and
+some English to explain that string if necessary.
+
+\1f