GNU Texinfo 4.2: 8. Cross References

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# 8. Cross References

Cross references are used to refer the reader to other parts of the same or different Texinfo files. In Texinfo, nodes and anchors are the places to which cross references can refer.

## What References Are For

Often, but not always, a printed document should be designed so that it can be read sequentially. People tire of flipping back and forth to find information that should be presented to them as they need it.

However, in any document, some information will be too detailed for the current context, or incidental to it; use cross references to provide access to such information. Also, an online help system or a reference manual is not like a novel; few read such documents in sequence from beginning to end. Instead, people look up what they need. For this reason, such creations should contain many cross references to help readers find other information that they may not have read.

In a printed manual, a cross reference results in a page reference, unless it is to another manual altogether, in which case the cross reference names that manual.

In Info, a cross reference results in an entry that you can follow using the Info ‘`f`’ command. (See Some advanced Info commands: (info)Help-Adv.)

The various cross reference commands use nodes (or anchors, see section `@anchor`) to define cross reference locations. This is evident in Info, in which a cross reference takes you to the specified location. TeX also uses nodes to define cross reference locations, but the action is less obvious. When TeX generates a DVI file, it records each node’s page number and uses the page numbers in making references. Thus, if you are writing a manual that will only be printed, and will not be used online, you must nonetheless write `@node` lines to name the places to which you make cross references.

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## 8.1 Different Cross Reference Commands

There are four different cross reference commands:

`@xref`

  Used to start a sentence in the printed manual saying ‘See …’ or an Info cross-reference saying ‘`*Note name: node.`’.

`@ref`

  Used within or, more often, at the end of a sentence; same as `@xref` for Info; produces just the reference in the printed manual without a preceding ‘See’.

`@pxref`

  Used within parentheses to make a reference that suits both an Info file and a printed book. Starts with a lower case ‘see’ within the printed manual. (‘`p`’ is for ‘parenthesis’.)

`@inforef`

  Used to make a reference to an Info file for which there is no printed manual.

(The `@cite` command is used to make references to books and manuals for which there is no corresponding Info file and, therefore, no node to which to point. See section `@cite`.)

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## 8.2 Parts of a Cross Reference

A cross reference command requires only one argument, which is the name of the node to which it refers. But a cross reference command may contain up to four additional arguments. By using these arguments, you can provide a cross reference name for Info, a topic description or section title for the printed output, the name of a different Info file, and the name of a different printed manual.

Here is a simple cross reference example:

    @xref{Node name}.

which produces

    *Note Node name::.

and

> See Section nnn [Node name], page ppp.

Here is an example of a full five-part cross reference:

    @xref{Node name, Cross Reference Name, Particular Topic,
    info-file-name, A Printed Manual}, for details.

which produces

    *Note Cross Reference Name: (info-file-name)Node name,
    for details.

in Info and

> See section “Particular Topic” in A Printed Manual, for details.

in a printed book.

The five possible arguments for a cross reference are:

1. The node or anchor name (required). This is the location to which the cross reference takes you. In a printed document, the location of the node provides the page reference only for references within the same document.
2. The cross reference name for the Info reference, if it is to be different from the node name. If you include this argument, it becomes the first part of the cross reference. It is usually omitted.
3. A topic description or section name. Often, this is the title of the section. This is used as the name of the reference in the printed manual. If omitted, the node name is used.
4. The name of the Info file in which the reference is located, if it is different from the current file. You need not include any ‘`.info`’ suffix on the file name, since Info readers try appending it automatically.
5. The name of a printed manual from a different Texinfo file.

The template for a full five argument cross reference looks like this:

    @xref{node-name, cross-reference-name, title-or-topic,
    info-file-name, printed-manual-title}.

Cross references with one, two, three, four, and five arguments are described separately following the description of `@xref`.

Write a node name in a cross reference in exactly the same way as in the `@node` line, including the same capitalization; otherwise, the formatters may not find the reference.

You can write cross reference commands within a paragraph, but note how Info and TeX format the output of each of the various commands: write `@xref` at the beginning of a sentence; write `@pxref` only within parentheses, and so on.

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## 8.3 `@xref`

The `@xref` command generates a cross reference for the beginning of a sentence. The Info formatting commands convert it into an Info cross reference, which the Info ‘`f`’ command can use to bring you directly to another node. The TeX typesetting commands convert it into a page reference, or a reference to another book or manual.

### What a Reference Looks Like and Requires

Most often, an Info cross reference looks like this:

    *Note node-name::.

or like this

    *Note cross-reference-name: node-name.

In TeX, a cross reference looks like this:

> See Section section-number [node-name], page page.

or like this

> See Section section-number [title-or-topic], page page.

The `@xref` command does not generate a period or comma to end the cross reference in either the Info file or the printed output. You must write that period or comma yourself; otherwise, Info will not recognize the end of the reference. (The `@pxref` command works differently. See section `@pxref`.)

> Please note: A period or comma must follow the closing brace of an `@xref`. It is required to terminate the cross reference. This period or comma will appear in the output, both in the Info file and in the printed manual.

`@xref` must refer to an Info node by name. Use `@node` to define the node (see section How to Write an `@node` Line).

`@xref` is followed by several arguments inside braces, separated by commas. Whitespace before and after these commas is ignored.

A cross reference requires only the name of a node; but it may contain up to four additional arguments. Each of these variations produces a cross reference that looks somewhat different.

> Please note: Commas separate arguments in a cross reference; avoid including them in the title or other part lest the formatters mistake them for separators.

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### 8.3.1 `@xref` with One Argument

The simplest form of `@xref` takes one argument, the name of another node in the same Info file. The Info formatters produce output that the Info readers can use to jump to the reference; TeX produces output that specifies the page and section number for you.

For example,

    @xref{Tropical Storms}.

produces

    *Note Tropical Storms::.

and

> See Section 3.1 [Tropical Storms], page 24.

(Note that in the preceding example the closing brace is followed by a period.)

You can write a clause after the cross reference, like this:

    @xref{Tropical Storms}, for more info.

which produces

    *Note Tropical Storms::, for more info.

and

> See Section 3.1 [Tropical Storms], page 24, for more info.

(Note that in the preceding example the closing brace is followed by a comma, and then by the clause, which is followed by a period.)

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### 8.3.2 `@xref` with Two Arguments

With two arguments, the second is used as the name of the Info cross reference, while the first is still the name of the node to which the cross reference points.

The template is like this:

    @xref{node-name, cross-reference-name}.

For example,

    @xref{Electrical Effects, Lightning}.

produces:

    *Note Lightning: Electrical Effects.

and

> See Section 5.2 [Electrical Effects], page 57.

(Note that in the preceding example the closing brace is followed by a period; and that the node name is printed, not the cross reference name.)

You can write a clause after the cross reference, like this:

    @xref{Electrical Effects, Lightning}, for more info.

which produces

    *Note Lightning: Electrical Effects, for more info.

and

> See Section 5.2 [Electrical Effects], page 57, for more info.

(Note that in the preceding example the closing brace is followed by a comma, and then by the clause, which is followed by a period.)

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### 8.3.3 `@xref` with Three Arguments

A third argument replaces the node name in the TeX output. The third argument should be the name of the section in the printed output, or else state the topic discussed by that section. Often, you will want to use initial upper case letters so it will be easier to read when the reference is printed. Use a third argument when the node name is unsuitable because of syntax or meaning.

Remember to avoid placing a comma within the title or topic section of a cross reference, or within any other section. The formatters divide cross references into arguments according to the commas; a comma within a title or other section will divide it into two arguments. In a reference, you need to write a title such as “Clouds, Mist, and Fog” without the commas.

Also, remember to write a comma or period after the closing brace of an `@xref` to terminate the cross reference. In the following examples, a clause follows a terminating comma.

The template is like this:

    @xref{node-name, cross-reference-name, title-or-topic}.

For example,

    @xref{Electrical Effects, Lightning, Thunder and Lightning},
    for details.

produces

    *Note Lightning: Electrical Effects, for details.

and

> See Section 5.2 [Thunder and Lightning], page 57, for details.

If a third argument is given and the second one is empty, then the third argument serves both. (Note how two commas, side by side, mark the empty second argument.)

    @xref{Electrical Effects, , Thunder and Lightning},
    for details.

produces

    *Note Thunder and Lightning: Electrical Effects, for details.

and

> See Section 5.2 [Thunder and Lightning], page 57, for details.

As a practical matter, it is often best to write cross references with just the first argument if the node name and the section title are the same, and with the first and third arguments if the node name and title are different.

Here are several examples from The GNU Awk User’s Guide:

    @xref{Sample Program}.
    @xref{Glossary}.
    @xref{Case-sensitivity, ,Case-sensitivity in Matching}.
    @xref{Close Output, , Closing Output Files and Pipes},
       for more information.
    @xref{Regexp, , Regular Expressions as Patterns}.

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### 8.3.4 `@xref` with Four and Five Arguments

In a cross reference, a fourth argument specifies the name of another Info file, different from the file in which the reference appears, and a fifth argument specifies its title as a printed manual.

Remember that a comma or period must follow the closing brace of an `@xref` command to terminate the cross reference. In the following examples, a clause follows a terminating comma.

The template is:

    @xref{node-name, cross-reference-name, title-or-topic,
    info-file-name, printed-manual-title}.

For example,

    @xref{Electrical Effects, Lightning, Thunder and Lightning,
    weather, An Introduction to Meteorology}, for details.

produces

    *Note Lightning: (weather)Electrical Effects, for details.

The name of the Info file is enclosed in parentheses and precedes the name of the node.

In a printed manual, the reference looks like this:

> See section “Thunder and Lightning” in An Introduction to Meteorology, for details.

The title of the printed manual is typeset in italics; and the reference lacks a page number since TeX cannot know to which page a reference refers when that reference is to another manual.

Often, you will leave out the second argument when you use the long version of `@xref`. In this case, the third argument, the topic description, will be used as the cross reference name in Info.

The template looks like this:

    @xref{node-name, , title-or-topic, info-file-name,
    printed-manual-title}, for details.

which produces

    *Note title-or-topic: (info-file-name)node-name, for details.

and

> See section title-or-topic in printed-manual-title, for details.

For example,

    @xref{Electrical Effects, , Thunder and Lightning,
    weather, An Introduction to Meteorology}, for details.

produces

    *Note Thunder and Lightning: (weather)Electrical Effects,
    for details.

and

> See section “Thunder and Lightning” in An Introduction to Meteorology, for details.

On rare occasions, you may want to refer to another Info file that is within a single printed manual—when multiple Texinfo files are incorporated into the same TeX run but make separate Info files. In this case, you need to specify only the fourth argument, and not the fifth.

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## 8.4 Naming a ‘Top’ Node

In a cross reference, you must always name a node. This means that in order to refer to a whole manual, you must identify the ‘Top’ node by writing it as the first argument to the `@xref` command. (This is different from the way you write a menu entry; see Referring to Other Info Files.) At the same time, to provide a meaningful section topic or title in the printed cross reference (instead of the word ‘Top’), you must write an appropriate entry for the third argument to the `@xref` command.

Thus, to make a cross reference to The GNU Make Manual, write:

    @xref{Top, , Overview, make, The GNU Make Manual}.

which produces

    *Note Overview: (make)Top.

and

> See section “Overview” in The GNU Make Manual.

In this example, ‘`Top`’ is the name of the first node, and ‘`Overview`’ is the name of the first section of the manual.

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## 8.5 `@ref`

`@ref` is nearly the same as `@xref` except that it does not generate a ‘See’ in the printed output, just the reference itself. This makes it useful as the last part of a sentence.

For example,

    For more information, see @ref{Hurricanes}.

produces

    For more information, see *Note Hurricanes::.

and

> For more information, see Section 8.2 [Hurricanes], page 123.

The `@ref` command sometimes leads writers to express themselves in a manner that is suitable for a printed manual but looks awkward in the Info format. Bear in mind that your audience will be using both the printed and the Info format.

For example,

    Sea surges are described in @ref{Hurricanes}.

produces

> Sea surges are described in Section 6.7 [Hurricanes], page 72.

in a printed document, and the following in Info:

    Sea surges are described in *Note Hurricanes::.

> Caution: You must write a period, comma, or right parenthesis immediately after an `@ref` command with two or more arguments. Otherwise, Info will not find the end of the cross reference entry and its attempt to follow the cross reference will fail. As a general rule, you should write a period or comma after every `@ref` command. This looks best in both the printed and the Info output.

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## 8.6 `@pxref`

The parenthetical reference command, `@pxref`, is nearly the same as `@xref`, but you use it only inside parentheses and you do not type a comma or period after the command’s closing brace. The command differs from `@xref` in two ways:

1. TeX typesets the reference for the printed manual with a lower case ‘see’ rather than an upper case ‘See’.
2. The Info formatting commands automatically end the reference with a closing colon or period.

Because one type of formatting automatically inserts closing punctuation and the other does not, you should use `@pxref` only inside parentheses as part of another sentence. Also, you yourself should not insert punctuation after the reference, as you do with `@xref`.

`@pxref` is designed so that the output looks right and works right between parentheses both in printed output and in an Info file. In a printed manual, a closing comma or period should not follow a cross reference within parentheses; such punctuation is wrong. But in an Info file, suitable closing punctuation must follow the cross reference so Info can recognize its end. `@pxref` spares you the need to use complicated methods to put a terminator into one form of the output and not the other.

With one argument, a parenthetical cross reference looks like this:

    … storms cause flooding (@pxref{Hurricanes}) …

which produces

    … storms cause flooding (*Note Hurricanes::) …

and

> … storms cause flooding (see Section 6.7 [Hurricanes], page 72) …

With two arguments, a parenthetical cross reference has this template:

    … (@pxref{node-name, cross-reference-name}) …

which produces

    … (*Note cross-reference-name: node-name.) …

and

> … (see Section nnn [node-name], page ppp) …

`@pxref` can be used with up to five arguments just like `@xref` (see section `@xref`).

> Please note: Use `@pxref` only as a parenthetical reference. Do not try to use `@pxref` as a clause in a sentence. It will look bad in either the Info file, the printed output, or both.

> Also, parenthetical cross references look best at the ends of sentences. Although you may write them in the middle of a sentence, that location breaks up the flow of text.

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## 8.7 `@inforef`

`@inforef` is used for cross references to Info files for which there are no printed manuals. Even in a printed manual, `@inforef` generates a reference directing the user to look in an Info file.

The command takes either two or three arguments, in the following order:

1. The node name.
2. The cross reference name (optional).
3. The Info file name.

Separate the arguments with commas, as with `@xref`. Also, you must terminate the reference with a comma or period after the ‘`}`’, as you do with `@xref`.

The template is:

    @inforef{node-name, cross-reference-name, info-file-name},

Thus,

    @inforef{Expert, Advanced Info commands, info},
    for more information.

produces

    *Note Advanced Info commands: (info)Expert,
    for more information.

and

> See Info file ‘`info`’, node ‘`Expert`’, for more information.

Similarly,

    @inforef{Expert, , info}, for more information.

produces

    *Note (info)Expert::, for more information.

and

> See Info file ‘`info`’, node ‘`Expert`’, for more information.

The converse of `@inforef` is `@cite`, which is used to refer to printed works for which no Info form exists. See section `@cite`.

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## 8.8 `@uref{url[, text][, replacement]}`

`@uref` produces a reference to a uniform resource locator (url). It takes one mandatory argument, the url, and two optional arguments which control the text that is displayed. In HTML output, `@uref` produces a link you can follow.

The second argument, if specified, is the text to display (the default is the url itself); in Info and DVI output, but not in HTML output, the url is also output.

The third argument, on the other hand, if specified is also the text to display, but the url is not output in any format. This is useful when the text is already sufficiently referential, as in a man page. If the third argument is given, the second argument is ignored.

The simple one argument form, where the url is both the target and the text of the link:

    The official GNU ftp site is @uref{ftp://ftp.gnu.org/gnu}.

produces:

    The official GNU ftp site is ftp://ftp.gnu.org/gnu.

An example of the two-argument form:

    The official @uref{ftp://ftp.gnu.org/gnu, GNU ftp site}
    holds programs and texts.

produces:

    The official GNU ftp site
    holds programs and texts.

that is, the Info output is this:

    The official GNU ftp site (ftp://ftp.gnu.org/gnu)
    holds programs and texts.

and the HTML output is this:

    The official <a href="ftp://ftp.gnu.org/gnu">GNU ftp site</a>
    holds programs and texts.

An example of the three-argument form:

    The @uref{/man.cgi/1/ls,,ls(1)} program …

produces:

    The ls(1) program …

but with HTML:

    The <a href="/man.cgi/1/ls">ls(1)</a> program …

To merely indicate a url without creating a link people can follow, use `@url` (see section `@url`).

Some people prefer to display url’s in the unambiguous format:

    <URL:http://host/path>

You can use this form in the input file if you wish. We feel it’s not necessary to clutter up the output with the extra ‘`<URL:`’ and ‘`>`’, since any software that tries to detect url’s in text already has to detect them without the ‘`<URL:`’ to be useful.

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