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.

8.1 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 Following cross-references: (info)Help-Xref.)

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.

8.2 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.)

8.3 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 or the topic description. If you include this argument, it becomes the first part of the cross reference. It is usually omitted; then the topic description (third argument) is used if it was specified; if that was omitted as well, the node name is used.
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.

8.4 @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.

8.4.1 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.)

Caution: 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.

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

8.4.2 @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.)

8.4.3 @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.)

8.4.4 @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}.

8.4.5 @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.

8.5 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.

8.6 @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, @pxref{This}, and @ref{That}.

produces in Info:

For more information, *note This::, and *note That::.

and in printed output:

For more information, see Section 1.1 [This], page 1, and Section 1.2 [That], page 2.

The @ref command sometimes tempts 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}.

looks ok in the printed output:

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

but is awkward to read in Info, “note” being a verb:

Sea surges are described in *note Hurricanes::.

You should write a period or comma immediately after an @ref command with two or more arguments. If there is no such following punctuation, makeinfo will generate a (grammatically incorrect) period in the Info output; otherwise, the cross-reference would fail completely, due to the current syntax of Info format.

In general, it is best to use @ref only when you need some word other than “see” to precede the reference. When “see” (or “See”) is ok, @xref and @pxref are preferable.

8.7 @pxref

The parenthetical reference command, @pxref, is nearly the same as @xref, but it is best used at the end of a sentence or before a closing parenthesis. 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, if necessary.

@pxref is designed so that the output looks right and works right at the end of a sentence or parenthetical phrase, 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).

In past versions of Texinfo, it was not allowed to write punctuation after a @pxref, so it could be used only before a right parenthesis. This is no longer the case, so now it can be used (for example) at the end of a sentence, where a lowercase “see” works best. For instance:

… For more information, @pxref{More}.

which outputs (in Info):

… For more information, *note More::.

This works fine. @pxref should only be followed by a comma, period, or right parenthesis; in other cases, makeinfo has to insert a period to make the cross-reference work correctly in Info, and that period looks wrong.

As a matter of general style, @pxref is best used at the ends of sentences. Although it technically works in the middle of a sentence, that location breaks up the flow of reading.

8.8 @inforef

@inforef is used for making cross references to Info documents—even from a printed manual. This might be because you want to refer to conditional @ifinfo text (see section Conditionally Visible Text), or because printed output is not available (perhaps because there is no Texinfo source), among other possibilities.

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},

For example,

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

produces (in Info):

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

and (in the printed output):

See Info file ‘info’, node ‘Advanced’, for more information.

(This particular example is not realistic, since the Info manual is written in Texinfo, so all formats are available.)

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

8.9 @url, @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.

@url is a synonym for @uref. Originally, @url had the meaning of @indicateurl (see section @indicateurl), but in actual practice it was misused the vast majority of the time. So we’ve changed the meaning.

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, if specified, is the text to display, but in this case 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.

If the url is long enough to cause problems with line breaking, you may find it useful to insert @/ at places where a line break would be acceptable (after ‘/’ characters, for instance). This tells TeX to allow (but not force) a line break at those places. See section @* and @/: Generate and Allow Line Breaks.

Here is an example of 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} program …

produces:

The ls program …

but with HTML:

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

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

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 include the ‘<URL:’ and ‘>’ in the output, since any software that tries to detect url’s in text already has to detect them without the ‘<URL:’ to be useful.

8.10 @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.

This document was generated by Aidan Kehoe on December 27, 2016 using texi2html 1.82.