In a Texinfo file, the commands that tell TeX how to typeset the
printed manual and tell makeinfo and
texinfo-format-buffer how to create an Info file are preceded
by @; they are called @-commands. For example,
@node is the command to indicate a node and @chapter
is the command to indicate the start of a chapter.
Please note: All the @-commands, with the exception of the
@TeX{} command, must be written entirely in lower case.
The Texinfo @-commands are a strictly limited set of constructs. The strict limits make it possible for Texinfo files to be understood both by TeX and by the code that converts them into Info files. You can display Info files on any terminal that displays alphabetic and numeric characters. Similarly, you can print the output generated by TeX on a wide variety of printers.
Depending on what they do or what arguments1 they take, you need to write @-commands on lines of their own or as part of sentences:
@quotation at the beginning of a line as
the only text on the line. (@quotation begins an indented
environment.)
@chapter at the beginning of a line
followed by the command's arguments, in this case the chapter title, on
the rest of the line. (@chapter creates chapter titles.)
@dots{} wherever you wish but usually
within a sentence. (@dots{} creates dots ...)
@code{sample-code} wherever you
wish (but usually within a sentence) with its argument,
sample-code in this example, between the braces. (@code
marks text as being code.)
@example on a line of its own; write the
body-text on following lines; and write the matching @end
command, @end example in this case, on a line of its own
after the body-text. (@example ... @end example
indents and typesets body-text as an example.) It's usually ok to
indent environment commands like this, but in complicated and
hard-to-define circumstances the extra spaces cause extra space to
appear in the output, so beware.
As a general rule, a command requires braces if it mingles among other
text; but it does not need braces if it starts a line of its own. The
non-alphabetic commands, such as @:, are exceptions to the rule;
they do not need braces.
As you gain experience with Texinfo, you will rapidly learn how to write the different commands: the different ways to write commands make it easier to write and read Texinfo files than if all commands followed exactly the same syntax. (For details about @-command syntax, see @-Command Syntax.)
The word argument comes from the way it is used in mathematics and does not refer to a dispute between two people; it refers to the information presented to the command. According to the Oxford English Dictionary, the word derives from the Latin for to make clear, prove; thus it came to mean `the evidence offered as proof', which is to say, `the information offered', which led to its mathematical meaning. In its other thread of derivation, the word came to mean `to assert in a manner against which others may make counter assertions', which led to the meaning of `argument' as a dispute.