texinfo: Conditional Commands

Conditionals

Conditional Not Commands

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18.1 Conditional Commands
=========================

Texinfo has an '@ifFORMAT' environment for each output format, to allow
conditional inclusion of text for a particular output format.

  '@ifinfo' begins segments of text that should be ignored by TeX when
it typesets the printed manual, and by 'makeinfo' when not producing
Info output.  The segment of text appears only in the Info file and, for
historical compatibility, the plain text output.

  The environments for the other formats are analogous, but without the
special historical case:

'@ifdocbook ... @end ifdocbook'
     Text to appear only in the Docbook output.

'@ifhtml ... @end ifhtml'
     Text to appear only in the HTML output.

'@ifplaintext ... @end ifplaintext'
     Text to appear only in the plain text output.

'@iftex ... @end iftex'
     Text to appear only in the printed manual.

'@ifxml ... @end ifxml'
     Text to appear only in the XML output.

  The '@if...' and '@end if...' commands must appear on lines by
themselves in your source file.  The newlines following the commands are
(more or less) treated as whitespace, so that the conditional text is
flowed normally into a surrounding paragraph.

  The '@if...' constructs are intended to conditionalize normal Texinfo
source; Note: Raw Formatter Commands, for using underlying format
commands directly.

  Here is an example showing all these conditionals:

     @iftex
     This text will appear only in the printed manual.
     @end iftex
     @ifinfo
     However, this text will appear only in Info and plain text.
     @end ifinfo
     @ifhtml
     And this text will only appear in HTML.
     @end ifhtml
     @ifplaintext
     Whereas this text will only appear in plain text.
     @end ifplaintext
     @ifxml
     Notwithstanding that this will only appear in XML.
     @end ifxml
     @ifdocbook
     Nevertheless, this will only appear in Docbook.
     @end ifdocbook

The preceding example produces the following line:

  However, this text will appear only in Info and plain text.

Notice that you only see one of the input lines, depending on which
version of the manual you are reading.

  In complex documents, you may want Texinfo to issue an error message
in some conditionals that should not ever be processed.  The
'@errormsg{TEXT}' command will do this; it takes one argument, the text
of the error message, which is expanded more or less as if it were Info
text.

  We mention '@errormsg{}' here even though it is not strictly related
to conditionals, since in practice it is most likely to be useful in
that context.  Technically, it can be used anywhere.  Note: External
Macro Processors, for a caveat regarding the line numbers which
'@errormsg' emits in TeX.