GNU Texinfo 4.2: 9. Marking Words and Phrases

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# 9. Marking Words and Phrases

In Texinfo, you can mark words and phrases in a variety of ways. The Texinfo formatters use this information to determine how to highlight the text. You can specify, for example, whether a word or phrase is a defining occurrence, a metasyntactic variable, or a symbol used in a program. Also, you can emphasize text, in several different ways.

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## 9.1 Indicating Definitions, Commands, etc.

Texinfo has commands for indicating just what kind of object a piece of text refers to. For example, metasyntactic variables are marked by `@var`, and code by `@code`. Since the pieces of text are labelled by commands that tell what kind of object they are, it is easy to change the way the Texinfo formatters prepare such text. (Texinfo is an intentional formatting language rather than a typesetting formatting language.)

For example, in a printed manual, code is usually illustrated in a typewriter font; `@code` tells TeX to typeset this text in this font. But it would be easy to change the way TeX highlights code to use another font, and this change would not affect how keystroke examples are highlighted. If straight typesetting commands were used in the body of the file and you wanted to make a change, you would need to check every single occurrence to make sure that you were changing code and not something else that should not be changed.

### Highlighting Commands are Useful

The highlighting commands can be used to extract useful information from the file, such as lists of functions or file names. It is possible, for example, to write a program in Emacs Lisp (or a keyboard macro) to insert an index entry after every paragraph that contains words or phrases marked by a specified command. You could do this to construct an index of functions if you had not already made the entries.

The commands serve a variety of purposes:

`@code{sample-code}`

  Indicate text that is a literal example of a piece of a program.

`@kbd{keyboard-characters}`

  Indicate keyboard input.

`@key{key-name}`

  Indicate the conventional name for a key on a keyboard.

`@samp{text}`

  Indicate text that is a literal example of a sequence of characters.

`@var{metasyntactic-variable}`

  Indicate a metasyntactic variable.

`@env{environment-variable}`

  Indicate an environment variable.

`@file{file-name}`

  Indicate the name of a file.

`@command{command-name}`

  Indicate the name of a command.

`@option{option}`

  Indicate a command-line option.

`@dfn{term}`

  Indicate the introductory or defining use of a term.

`@cite{reference}`

  Indicate the name of a book.

`@acronym{acronym}`

  Indicate an acronym.

`@url{uniform-resource-locator}`

  Indicate a uniform resource locator for the World Wide Web.

`@email{email-address[, displayed-text]}`

  Indicate an electronic mail address.

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### 9.1.1 `@code`{sample-code}

Use the `@code` command to indicate text that is a piece of a program and which consists of entire syntactic tokens. Enclose the text in braces.

Thus, you should use `@code` for an expression in a program, for the name of a variable or function used in a program, or for a keyword in a programming language.

Use `@code` for command names in languages that resemble programming languages, such as Texinfo. For example, `@code` and `@samp` are produced by writing ‘`@code{@@code}`’ and ‘`@code{@@samp}`’ in the Texinfo source, respectively.

It is incorrect to alter the case of a word inside an `@code` command when it appears at the beginning of a sentence. Most computer languages are case sensitive. In C, for example, `Printf` is different from the identifier `printf`, and most likely is a misspelling of it. Even in languages which are not case sensitive, it is confusing to a human reader to see identifiers spelled in different ways. Pick one spelling and always use that. If you do not want to start a sentence with a command name written all in lower case, you should rearrange the sentence.

In the printed manual, `@code` causes TeX to typeset the argument in a typewriter face. In the Info file, it causes the Info formatting commands to use single quotation marks around the text.

For example,

    The function returns @code{nil}.

produces this in the printed manual:

> The function returns `nil`.

Here are some cases for which it is preferable not to use `@code`:

- For shell command names such as `ls` (use `@command`).
- For shell options such as ‘`-c`’ when such options stand alone (use `@option`).
- Also, an entire shell command often looks better if written using `@samp` rather than `@code`. In this case, the rule is to choose the more pleasing format.
- For environment variable such as `TEXINPUTS` (use `@env`).
- For a string of characters shorter than a syntactic token. For example, if you are writing about ‘`goto-ch`’, which is just a part of the name for the `goto-char` Emacs Lisp function, you should use `@samp`.
- In general, when writing about the characters used in a token; for example, do not use `@code` when you are explaining what letters or printable symbols can be used in the names of functions. (Use `@samp`.) Also, you should not use `@code` to mark text that is considered input to programs unless the input is written in a language that is like a programming language. For example, you should not use `@code` for the keystroke commands of GNU Emacs (use `@kbd` instead) although you may use `@code` for the names of the Emacs Lisp functions that the keystroke commands invoke.

Since `@command`, `@option`, and `@env` were introduced relatively recently, it is acceptable to use `@code` or `@samp` for command names, options, and environment variables. The new commands allow you to express the markup more precisely, but there is no real harm in using the older commands, and of course the long-standing manuals do so.

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### 9.1.2 `@kbd`{keyboard-characters}

Use the `@kbd` command for characters of input to be typed by users. For example, to refer to the characters `M-a`, write

    @kbd{M-a}

and to refer to the characters `M-x shell`, write

    @kbd{M-x shell}

The `@kbd` command has the same effect as `@code` in Info, but by default produces a different font (slanted typewriter instead of normal typewriter) in the printed manual, so users can distinguish the characters they are supposed to type from those the computer outputs.

Since the usage of `@kbd` varies from manual to manual, you can control the font switching with the `@kbdinputstyle` command. This command has no effect on Info output. Write this command at the beginning of a line with a single word as an argument, one of the following:

‘`code`’

  Always use the same font for `@kbd` as `@code`.

‘`example`’

  Use the distinguishing font for `@kbd` only in `@example` and similar environments.

‘`distinct`’

  (the default) Always use the distinguishing font for `@kbd`.

You can embed another @-command inside the braces of an `@kbd` command. Here, for example, is the way to describe a command that would be described more verbosely as “press an ‘`r`’ and then press the <RET> key”:

    @kbd{r @key{RET}}

This produces: `r <RET>`

You also use the `@kbd` command if you are spelling out the letters you type; for example:

    To give the @code{logout} command,
    type the characters @kbd{l o g o u t @key{RET}}.

This produces:

> To give the `logout` command, type the characters `l o g o u t <RET>`.

(Also, this example shows that you can add spaces for clarity. If you really want to mention a space character as one of the characters of input, write `@key{SPC}` for it.)

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### 9.1.3 `@key`{key-name}

Use the `@key` command for the conventional name for a key on a keyboard, as in:

    @key{RET}

You can use the `@key` command within the argument of an `@kbd` command when the sequence of characters to be typed includes one or more keys that are described by name.

For example, to produce `C-x <ESC>` you would type:

    @kbd{C-x @key{ESC}}

Here is a list of the recommended names for keys:

> `SPC`

>   Space

> `RET`

>   Return

> `LFD`

>   Linefeed (however, since most keyboards nowadays do not have a Linefeed key, it might be better to call this character `C-j`.

> `TAB`

>   Tab

> `BS`

>   Backspace

> `ESC`

>   Escape

> `DEL`

>   Delete

> `SHIFT`

>   Shift

> `CTRL`

>   Control

> `META`

>   Meta

There are subtleties to handling words like ‘meta’ or ‘ctrl’ that are names of modifier keys. When mentioning a character in which the modifier key is used, such as `Meta-a`, use the `@kbd` command alone; do not use the `@key` command; but when you are referring to the modifier key in isolation, use the `@key` command. For example, write ‘`@kbd{Meta-a}`’ to produce `Meta-a` and ‘`@key{META}`’ to produce <META>.

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### 9.1.4 `@samp`{text}

Use the `@samp` command to indicate text that is a literal example or ‘sample’ of a sequence of characters in a file, string, pattern, etc. Enclose the text in braces. The argument appears within single quotation marks in both the Info file and the printed manual; in addition, it is printed in a fixed-width font.

    To match @samp{foo} at the end of the line,
    use the regexp @samp{foo$}.

produces

> To match ‘`foo`’ at the end of the line, use the regexp ‘`foo$`’.

Any time you are referring to single characters, you should use `@samp` unless `@kbd` or `@key` is more appropriate. Also, you may use `@samp` for entire statements in C and for entire shell commands—in this case, `@samp` often looks better than `@code`. Basically, `@samp` is a catchall for whatever is not covered by `@code`, `@kbd`, or `@key`.

Only include punctuation marks within braces if they are part of the string you are specifying. Write punctuation marks outside the braces if those punctuation marks are part of the English text that surrounds the string. In the following sentence, for example, the commas and period are outside of the braces:

    In English, the vowels are @samp{a}, @samp{e},
    @samp{i}, @samp{o}, @samp{u}, and sometimes
    @samp{y}.

This produces:

> In English, the vowels are ‘`a`’, ‘`e`’, ‘`i`’, ‘`o`’, ‘`u`’, and sometimes ‘`y`’.

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### 9.1.5 `@verb`{<char>text<char>}

Use the `@verb` command to print a verbatim sequence of characters.

Like LaTeX’s `\verb` command, the verbatim text can be quoted using any unique delimiter character. Enclose the verbatim text, including the delimiters, in braces. Text is printed in a fixed-width font:

    How many @verb{|@|}-escapes does one need to print this
    @verb{.@a @b @c.} string or @verb{+@'e?`!`{}\+} this?

produces

    How many @ -escapes does one need to print this
    @a @b @c string or these @'e?`{}!`\ this?

This is in contrast to `@samp` (see the previous section), whose argument is normal Texinfo text, where the characters `@{}` are special; with `@verb`, nothing is special except the delimiter character you choose.

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### 9.1.6 `@var`{metasyntactic-variable}

Use the `@var` command to indicate metasyntactic variables. A metasyntactic variable is something that stands for another piece of text. For example, you should use a metasyntactic variable in the documentation of a function to describe the arguments that are passed to that function.

Do not use `@var` for the names of particular variables in programming languages. These are specific names from a program, so `@code` is correct for them (see section `@code`{sample-code}). For example, the Emacs Lisp variable `texinfo-tex-command` is not a metasyntactic variable; it is properly formatted using `@code`.

Do not use `@var` for environment variables either; `@env` is correct for them (see the next section).

The effect of `@var` in the Info file is to change the case of the argument to all upper case. In the printed manual and HTML output, the argument is printed in slanted type.

For example,

    To delete file @var{filename},
    type @samp{rm @var{filename}}.

produces

> To delete file filename, type ‘`rm filename`’.

(Note that `@var` may appear inside `@code`, `@samp`, `@file`, etc.)

Write a metasyntactic variable all in lower case without spaces, and use hyphens to make it more readable. Thus, the Texinfo source for the illustration of how to begin a Texinfo manual looks like this:

    \input texinfo
    @@setfilename @var{info-file-name}
    @@settitle @var{name-of-manual}

This produces:

    \input texinfo
    @setfilename info-file-name
    @settitle name-of-manual

In some documentation styles, metasyntactic variables are shown with angle brackets, for example:

    …, type rm <filename>

However, that is not the style that Texinfo uses. (You can, of course, modify the sources to ‘`texinfo.tex`’ and the Info formatting commands to output the `<…>` format if you wish.)

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### 9.1.7 `@env`{environment-variable}

Use the `@env` command to indicate environment variables, as used by many operating systems, including GNU. Do not use it for metasyntactic variables; use `@var` instead (see the previous section).

`@env` is equivalent to `@code` in its effects. For example:

    The @env{PATH} environment variable …

produces

> The `PATH` environment variable …

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### 9.1.8 `@file`{file-name}

Use the `@file` command to indicate text that is the name of a file, buffer, or directory, or is the name of a node in Info. You can also use the command for file name suffixes. Do not use `@file` for symbols in a programming language; use `@code`.

Currently, `@file` is equivalent to `@samp` in its effects. For example,

    The @file{.el} files are in
    the @file{/usr/local/emacs/lisp} directory.

produces

> The ‘`.el`’ files are in the ‘`/usr/local/emacs/lisp`’ directory.

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### 9.1.9 `@command`{command-name}

Use the `@command` command to indicate command names, such as `ls` or `cc`.

`@command` is equivalent to `@code` in its effects. For example:

    The command @command{ls} lists directory contents.

produces

> The command `ls` lists directory contents.

You should write the name of a program in the ordinary text font, rather than using `@command`, if you regard it as a new English word, such as ‘Emacs’ or ‘Bison’.

When writing an entire shell command invocation, as in ‘`ls -l`’, you should use either `@samp` or `@code` at your discretion.

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### 9.1.10 `@option`{option-name}

Use the `@option` command to indicate a command-line option; for example, ‘`-l`’ or ‘`--version`’ or ‘`--output=filename`’.

`@option` is equivalent to `@samp` in its effects. For example:

    The option @option{-l} produces a long listing.

produces

> The option ‘`-l`’ produces a long listing.

In tables, putting options inside `@code` produces a more pleasing effect.

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### 9.1.11 `@dfn`{term}

Use the `@dfn` command to identify the introductory or defining use of a technical term. Use the command only in passages whose purpose is to introduce a term which will be used again or which the reader ought to know. Mere passing mention of a term for the first time does not deserve `@dfn`. The command generates italics in the printed manual, and double quotation marks in the Info file. For example:

    Getting rid of a file is called @dfn{deleting} it.

produces

> Getting rid of a file is called deleting it.

As a general rule, a sentence containing the defining occurrence of a term should be a definition of the term. The sentence does not need to say explicitly that it is a definition, but it should contain the information of a definition—it should make the meaning clear.

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### 9.1.12 `@cite`{reference}

Use the `@cite` command for the name of a book that lacks a companion Info file. The command produces italics in the printed manual, and quotation marks in the Info file.

If a book is written in Texinfo, it is better to use a cross reference command since a reader can easily follow such a reference in Info. See section `@xref`.

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### 9.1.13 `@acronym`{acronym}

Use the `@acronym` command for abbreviations written in all capital letters, such as ‘NASA’. The abbreviation is given as the single argument in braces, as in ‘`@acronym{NASA}`’. As a matter of style, or for particular abbreviations, you may prefer to use periods, as in ‘`@acronym{F.B.I.}`’.

In TeX and HTML, the argument is printed in a slightly smaller font size. In Info or plain text output, this command changes nothing.

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### 9.1.14 `@url`{uniform-resource-locator}

Use the `@url` command to indicate a uniform resource locator on the World Wide Web. This is analogous to `@file`, `@var`, etc., and is purely for markup purposes. It does not produce a link you can follow in HTML output (use the `@uref` command for that, see section `@uref`). It is useful for url’s which do not actually exist. For example:

    For example, the url might be @url{http://example.org/path}.

which produces:

    For example, the url might be http://example.org/path.

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### 9.1.15 `@email`{email-address[, displayed-text]}

Use the `@email` command to indicate an electronic mail address. It takes one mandatory argument, the address, and one optional argument, the text to display (the default is the address itself).

In Info and TeX, the address is shown in angle brackets, preceded by the text to display if any. In HTML output, `@email` produces a ‘`mailto`’ link that usually brings up a mail composition window. For example:

    Send bug reports to @email{bug-texinfo@@gnu.org},
    suggestions to the @email{bug-texinfo@@gnu.org, same place}.

produces

    Send bug reports to bug-texinfo@gnu.org,
    suggestions to the same place.

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## 9.2 Emphasizing Text

Usually, Texinfo changes the font to mark words in the text according to what category the words belong to; an example is the `@code` command. Most often, this is the best way to mark words. However, sometimes you will want to emphasize text without indicating a category. Texinfo has two commands to do this. Also, Texinfo has several commands that specify the font in which TeX will typeset text. These commands have no effect on Info and only one of them, the `@r` command, has any regular use.

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### 9.2.1 `@emph`{text} and `@strong`{text}

The `@emph` and `@strong` commands are for emphasis; `@strong` is stronger. In printed output, `@emph` produces italics and `@strong` produces bold.

For example,

    @quotation
    @strong{Caution:} @samp{rm * .[^.]*} removes @emph{all}
    files in the directory.
    @end quotation

produces:

         *Caution*: `rm * .[^.]*' removes _all_
         files in the directory.

The `@strong` command is seldom used except to mark what is, in effect, a typographical element, such as the word ‘Caution’ in the preceding example.

In the Info output, `@emph` surrounds the text with underscores (‘`_`’), and `@strong` puts asterisks around the text.

> Caution: Do not use `@strong` with the word ‘`Note`’; Info will mistake the combination for a cross reference. Use a phrase such as Please note or Caution instead.

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### 9.2.2 `@sc`{text}: The Small Caps Font

Use the ‘`@sc`’ command to set text in the printed and the HTML output in A SMALL CAPS FONT and set text in the Info file in upper case letters. Write the text you want to be in small caps (where possible) between braces in lower case, like this:

    The @sc{acm} and @sc{ieee} are technical societies.

This produces:

    The ACM and IEEE are technical societies.

TeX typesets the small caps font in a manner that prevents the letters from ‘jumping out at you on the page’. This makes small caps text easier to read than text in all upper case—but it’s usually better to use regular mixed case anyway. The Info formatting commands set all small caps text in upper case. In HTML, the text is upper-cased and a smaller font is used to render it.

If the text between the braces of an `@sc` command is uppercase, TeX typesets in FULL-SIZE CAPITALS. Use full-size capitals sparingly, if ever, and since it’s redundant to mark all-uppercase text with `@sc`, `makeinfo` warns about such usage.

You may also use the small caps font for a jargon word such as ATO (a NASA word meaning ‘abort to orbit’).

There are subtleties to using the small caps font with a jargon word such as CDR, a word used in Lisp programming. In this case, you should use the small caps font when the word refers to the second and subsequent elements of a list (the CDR of the list), but you should use ‘`@code`’ when the word refers to the Lisp function of the same spelling.

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### 9.2.3 Fonts for Printing, Not Info

Texinfo provides four font commands that specify font changes in the printed manual but have no effect in the Info file. `@i` requests italic font (in some versions of TeX, a slanted font is used), `@b` requests bold face, `@t` requests the `fixed-width`, typewriter-style font used by `@code`, and `@r` requests a roman font, which is the usual font in which text is printed. All four commands apply to an argument that follows, surrounded by braces.

Only the `@r` command has much use: in example programs, you can use the `@r` command to convert code comments from the fixed-width font to a roman font. This looks better in printed output.

For example,

    @lisp
    (+ 2 2)    ; @r{Add two plus two.}
    @end lisp

produces

    (+ 2 2)    ; Add two plus two.

If possible, you should avoid using the other three font commands. If you need to use one, it probably indicates a gap in the Texinfo language.

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