texinfo: Command Syntax

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A.1 @-Command Syntax
====================

The character '@' is used to start all Texinfo commands.  (It has the
same meaning that '\' has in plain TeX.)  Texinfo has four types of
@-command:

1. Non-alphabetic commands.
     These commands consist of an @ followed by a punctuation mark or
     other character that is not part of the Latin alphabet.
     Non-alphabetic commands are almost always part of the text within a
     paragraph.  The non-alphabetic commands include '@@', '@{', '@}',
     '@.', '@SPACE', most of the accent commands, and many more.

2. Alphabetic commands that do not require arguments.
     These commands start with @ followed by a word followed by a left
     and right- brace.  These commands insert special symbols in the
     document; they do not take arguments.  Some examples: '@dots{}' =>
     '...', '@equiv{}' => '==', '@TeX{}' => 'TeX', and '@bullet{}' =>
     '*'.

3. Alphabetic commands that require arguments within braces.
     These commands start with @ followed by a letter or a word,
     followed by an argument within braces.  For example, the command
     '@dfn' indicates the introductory or defining use of a term; it is
     used as follows: 'In Texinfo, @@-commands are @dfn{mark-up}
     commands.'

4. Alphabetic commands that occupy an entire line.
     These commands occupy an entire line.  The line starts with @,
     followed by the name of the command (a word); for example,
     '@center' or '@cindex'.  If no argument is needed, the word is
     followed by the end of the line.  If there is an argument, it is
     separated from the command name by a space.  Braces are not used.

  Whitespace following an @-command name are optional and (usually)
ignored if present.  The exceptions are contexts whee whitespace is
significant, e.g., an '@example' environment.

  Thus, the alphabetic commands fall into classes that have different
argument syntaxes.  You cannot tell to which class a command belongs by
the appearance of its name, but you can tell by the command's meaning:
if the command stands for a glyph, it is in class 2 and does not require
an argument; if it makes sense to use the command among other text as
part of a paragraph, the command is in class 3 and must be followed by
an argument in braces; otherwise, it is in class 4 and uses the rest of
the line as its argument.

  The purpose of having a different syntax for commands of classes 3
and 4 is to make Texinfo files easier to read, and also to help the GNU
Emacs paragraph and filling commands work properly.  There is only one
exception to this rule: the command '@refill', which is always used at
the end of a paragraph immediately following the final period or other
punctuation character.  '@refill' takes no argument and does _not_
require braces.  '@refill' never confuses the Emacs paragraph commands
because it cannot appear at the beginning of a line.  It is also no
longer needed, since all formatters now refill paragraphs automatically.