The data to make an index come from many individual indexing commands scattered throughout the Texinfo source file. Each command says to add one entry to a particular index; after formatting, the index will give the current page number or node name as the reference.
An index entry consists of an indexing command at the beginning of a line followed, on the rest of the line, by the entry.
For example, this section begins with the following five entries for the concept index:
@cindex Defining indexing entries @cindex Index entries @cindex Entries for an index @cindex Specifying index entries @cindex Creating index entries
Each predefined index has its own indexing command---@cindex
for the concept index, @findex for the function index, and so
on.
Concept index entries consist of text. The best way to write an index is to choose entries that are terse yet clear. If you can do this, the index often looks better if the entries are not capitalized, but written just as they would appear in the middle of a sentence. (Capitalize proper names and acronyms that always call for upper case letters.) This is the case convention we use in most GNU manuals' indices.
If you don't see how to make an entry terse yet clear, make it longer and clear--not terse and confusing. If many of the entries are several words long, the index may look better if you use a different convention: to capitalize the first word of each entry. But do not capitalize a case-sensitive name such as a C or Lisp function name or a shell command; that would be a spelling error.
Whichever case convention you use, please use it consistently!
Entries in indices other than the concept index are symbol names in programming languages, or program names; these names are usually case-sensitive, so use upper and lower case as required for them.
By default, entries for a concept index are printed in a small roman
font and entries for the other indices are printed in a small
@code font. You may change the way part of an entry is
printed with the usual Texinfo commands, such as @file for
file names and @emph for emphasis (see section Marking Words and Phrases).
The six indexing commands for predefined indices are:
@cindex concept
@findex function
@vindex variable
@kindex keystroke
@pindex program
@tindex data type
Caution: Do not use a colon in an index entry. In Info, a colon separates the menu entry name from the node name. An extra colon confuses Info. See section The Parts of a Menu, for more information about the structure of a menu entry.
If you write several identical index entries in different places in a Texinfo file, the index in the printed manual will list all the pages to which those entries refer. However, the index in the Info file will list only the node that references the first of those index entries. Therefore, it is best to write indices in which each entry refers to only one place in the Texinfo file. Fortunately, this constraint is a feature rather than a loss since it means that the index will be easy to use. Otherwise, you could create an index that lists several pages for one entry and your reader would not know to which page to turn. If you have two identical entries for one topic, change the topics slightly, or qualify them to indicate the difference.
You are not actually required to use the predefined indices for their
canonical purposes. For example, suppose you wish to index some C
preprocessor macros. You could put them in the function index along
with actual functions, just by writing @findex commands for
them; then, when you print the "Function Index" as an unnumbered
chapter, you could give it the title `Function and Macro Index' and
all will be consistent for the reader. Or you could put the macros in
with the data types by writing @tindex commands for them, and
give that index a suitable title so the reader will understand.
(See section Index Menus and Printing an Index.)