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## 4.1 Eventually, I decided to write my first index style. How can I start?

Congratulations! You have made a good decision, indeed.

For a first impression, how a style file can be written from scratch reference the tutorial that comes with this distribution. It is written as a guided step-by-step practicing exercise and you can learn the basic concepts quite easily.

Afterwards, the best starting point is to make a copy of the template file that contains all the necessary commands that are needed to make a makeindex-like index. You can find it in the subdirectory markup/tex of the module library. Starting from this template you can remove or add commands as necessary.

Additionally, consult the library of predefined index style modules that comes with this distribution. Solutions for most of the typical problems can be found there, such as a module for doing case-insensitive sorting rules, or a typical TeX-like markup. Most of the time is is enough to include some of these modules and add a few additional commands.

Maybe some of the examples coming with the test-suite are good examples of how unusual index style files can be written.

Thus, there are many ways to learn writing an index style file. But it is very easy and after some experience you can process indexes your friends will be jealous of.

## 4.2 How to write my first index style?

Copy the file tex/makeidx.xdy from the library to your local directory. It is documented in in a way that should make it easy to fill in new commands or remove or modify others.

## 4.3 How works the actual key feature of makeindex with xindy?

The treatment of the actual key (usually denoted with @, the at-sign) has changed with xindy. Specifying index entries with a specific markup can be done in makeindex with the actual key. The makeindex-3 system and xindy offer the merge- and sort-rules to transform a key into different representations, limiting the need to specify an actual key. For example they support a style of writing

 \index{\bf{VIP}} 

which can be transformed with a rule like

 (merge-rule "\bf{$$.*$$}" "\1" :again :bregexp) 

which removes the macro definition for merging and sorting keywords, but keeping the original definition for markup purposes. Therefore we don't need any actual keys for all keywords written in boldface.

The makeindex behaviour, that the two keywords

 \index{VIP} \index{VIP@\bf{VIP}} 

are seen as two distinct index entries, can be simulated using the following definition:

 (merge-rule "\bf{$$.*$$}" "\1~e" :again :bregexp) 

This rule tells xindy to remove the boldface macro for merging and sorting purposes but defines the replacement to include the special character ~e, which is the last character in the alphabet (ISO-Latin in our case). This makes xindy treat them as different keywords and positions the boldface keyword right behind the one without any markup. Thus we receive the following mapping:

 Keyword: Merged and sorted as: Appears in the index as: VIP VIP VIP \bf{VIP} VIP~e \bf{VIP} 

With this new style of writing keywords and defining their markup, the need to explicitly specifying the print key (aka. actual key) has convinced us to remove the makeindex way of defining keywords.

## 4.4 I want to process an index for my native language. What must I do?

What makes makeindex hardly usable in non-English speaking countries is its lack of support of language specific alphabets and sort orderings. For example, many roman languages such as Italian, French, Portuguese or Spanish contain accented letters such as À, Á, ñ. Other languages from northern Europe have letters like Ä, Ø, æ or ß which often can't even be processed by many index processors let alone sorting them correctly into an index.

Two problems must be solved when processing indexes with a new languages:

1. The sort ordering of the indexed terms must be specified in an appropriate manner. This problem can be solved using the so-called keyword mappings.
2. The letter groups that partition the indexed terms into separate sections must be specified.

The xindy system can be configured to process these alphabets by defining sort and merge rules that allow expressing language specific rules.

The keyword mappings are as follows: The merge key is generated from the main key with the so called merge mapping. The merge mapping can be specified with the command merge-rule. The sort key is derived from the merge key using the sort mapping specified with the sort-rule command. The following scheme shows this mapping process:

The index style commands accomplishing this task are sort-rule and merge-rule. One example of such a rule would be

 (sort-rule "ä" "ae") 

defining that a word containing the umlaut-a will be sorted as if it contained the letters ae instead. This is one form of how the umlaut-a (ä) is sorted into german indexes. With an appropriate set of rules on can express the complete rules of a specific language.

An example of how an appropriate mapping for some of the Roman languages could look like is:

 (sort-rule "à" "a") (sort-rule "á" "a") (sort-rule "ã" "a") (sort-rule "è" "e") (sort-rule "é" "e") (sort-rule "ç" "c") 

This makes the accented letters be sorted as their unaccented counterparts, yielding the desired sort ordering.

Sometimes it is necessary to specify keyword mappings that tell the system to put something behind something else. For instance, we'd like to map the character ö behind the letter o. No problem if you use the special characters ~b and ~e which are called the beginning and ending characters. The first letter lexicographically precedes all other letters whereas the latter one comes after all others. Our mapping problem can now be specified as follows.

 (sort-rule "ö" "o~e") 

Now the ö is directly positioned after the o but before p.

See the manual for a detailed description of this feature. Also be informed that the keyword mappings can be specified with regular expressions. Rules of the form

 (merge-rule "[-\$()]" "") 

are possible. This on removes all letters of the defined letter class. Regular expression substitutions are possible as well. Refer to the manual for an exact description.

## 4.5 In my index the capitalized words appear after the lowercase words. Why?

The default sort ordering sorts letters according to their ordinal number in the ISO Latin alphabet. As a consequence the lowercase letters appear before the uppercase letters. To sort them case-insensitively use the command

 (require "lang/latin/caseisrt.xdy") 

This module defines the appropriate sort rules for the letters A-Z' for latin-based alphabets. If your language has more letters simply add the missing ones into your style file. Have a look at the module to see how to the sort rules are defined.

## 4.6 In my index there are no letter groups, yet!

Letter groups for latin based alphabets can be defined with the command

 (require "lang/latin/letgroup.xdy") 

If your language needs additional letter groups you can insert them into the previously defined letter group with inserting definitions of the following form:

 (define-letter-group "ly" :after "l" :before "m") (define-letter-group "ny" :after "n" :before "o") 

This adds two more letter groups to the latin alphabet. Group ly is inserted between l and m, and ny is inserted between n and o. This is how two additional letters of the Hungarian alphabet can be inserted.

## 4.7 How can I get rid of any formatting information in the keyword?

Assume you have index entries containing arbitrary formatting information. For example you write your index entries in TeX in the following form:

 \index{\bf{In boldface please}} 

To avoid specifying for each index entry the print key separately as can be done with the following command

 \index{In boldface please@\bf{In boldface please}} 

 (merge-rule "\\bf *{(.*)}" "\1" :eregexp :again) 

This extended regular expression matches all strings that are surrounded by this formatting command and in the merge phase the formatting command is simply stripped off. Thus, you don't need to write an explicit print key anymore.

If for some reason the same word appears more than once in the index, each time having another markup tag as in the following example

 index {\tt index} 

you must be warned that a rule like

 (merge-rule "{\\tt *(.*)}" "\1" :eregexp :again) 

is probably not correct. In this case the above strings are both mapped into the string index thus joining their location references into one index entry. This happens because the result of the merge mapping is used as the equality citerium which views both keywords as equal. To avoid this you should specify instead

 (merge-rule "{\\tt *(.*)}" "\1~e" :eregexp :again) 

With the additional meta character ~e the substitution of the second key word is placed after the first one making them different index entries. If the second keyword should appear first, use ~b instead.

## 4.8 In my index the word -foo appears before bar. What must I do?

Especially for hierarchical indexes sometimes the result is not as expected due to special characters appearing in the keyword. In the following example the word card' should appear before -eyed' since the hyphen should not count as an ordinary character by means of sorting.

 green -eyed 12 card 15 

This is especially problematic if the list of words on the second level is very long. To make the hyphen be simply ignored during the sorting process you should specify the following command in the index style:

 (sort-rule "-" "") 

This makes -eyed' be sorted as eyed' thus making it appear after card' as desired.

## 4.9 I want to use letter ordering instead of word ordering in my index.

According to the Chicago Manual of Style there exist two different schemes of sorting word lists. In word ordering a blank precedes any letter in the alphabet, whereas in letter ordering it does not count at all. The following example borrowed from the makeindex man-page illustrates the difference:

 Word Order: Letter Order: sea lion seal seal sea lion 

By default, xindy uses word ordering. To use letter ordering include the appropriate module with the following command:

 (require "ord/letorder.xdy") 

It actually defines the following command:

 (sort-rule " " "") 

This simply removes all blanks from the keyword resulting in the desired behaviour.

## 4.10 My document does not have page numbers, but a different scheme. What must I do?

The ability to deal with user-definable location structures is one of the most important new features of xindy. Many documents have a document structure that is not based on page numbers. Typical examples are manuals or appendices that come with a chapter/page-per-chapter numbering scheme, URLs, Bible verses, etc. One can even imagine the Greek alphabet as possibly appearing in a location reference. In our analysis we have found many interesting examples of location references that made us to develop the concept of location classes.

A location class is defined by a sequence of alphabets. An alphabet can be the set of arabic numbers (0, 1, 2, ...) or the roman numerals (i, ii, iii, ...). These are built-in alphabets in xindy. Addtionally, one can define more alphabets in the index style with a command like

  (define-alphabet "weekdays"
("mon" "tue" "wed" "thu" "fri" "sat" "sun"))


Based on alphabets one can now compose a location class as follows:

  (define-location-class "weekday-hours"
("weekday" :sep ":" "arabic-numbers"))


This class description indicates that all location refernces matching this template are viewed as correct instances of this class. Here :sep makes the dot serving as a separation string separation the alphabets from each other. Example instances of this class are:

mon:23, thu:45, sun:17


For more detailed information consult the description of the command define-location-class in the reference manual.

## 4.11 I don't want to have ranges in my index. What can I do?

By default, xindy joins three successive location references into a range. Ranges are used as an abbrevation for a long sequence of location references. For exmaple the sequence

12, 13, 14, 15, 16


would be shorter represented as

12-16


If you don't want to have ranges, simply define your location class in the form

  (define-location-class ... :min-range-length none)


The argument :min-range-length none avoids forming of ranges. Arbitrary numbers instead of none define the minimum length of a sequence of location references that are needed to form a range. xindys default value is 2.

## 4.12 I want to markup ranges of different length differently. How do I accomplish this?

A common way of tagging ranges is as follows: a range of length 1 is printed with the starting page number and the suffix f.', those of length 2 with suffix ff.', and all others in the form X--Y'.

Assume we want to do this for the location class pagenums we can specify the markup as follows:

 (markup-range :class "pagenums" :close "f." :length 1 :ignore-end) (markup-range :class "pagenums" :close "ff." :length 2 :ignore-end) (markup-range :class "pagenums" :sep "--") 

The first command indicates that a range (X,Y) of length 1 should be printed in the form Xf., a range of length 2 as Xff. and all others in the form X--Y. The switch :ignore-end causes the end of range location reference Y to be suppressed in the resulting output.

## 4.13 I need to suppress some of the markup tags. How can I do this?

Sometimes it is necessary to hide some of the parts of the index. If you have a text formatter that allows comments or macros that possibly expand to nothing, just define appropriate markup that makes things invisible to the formatter. For example, with TeX you can define a macro like this

 \def\ignore#1{} 

If you additionally define markup like this

 (markup-index :open "\ignore{" :close "}") 

you can throw away the complete index if you like, which would be a real pity!

## 4.14 Whats it all about those cross references?

Cross references are references pointing to an item in the index itself. Typical examples are:

 foo-bar see baz 

With makeindex cross references could be specified with the encapsulation mechanism. This has completely been removed in xindy and we have made cross references real first-class objects.

In xindy one can declare different cross reference classes, whose purpose is (a) to make all instances of a certain class appear next to each other, and (b) to specify appropriate markup with them.

@begin-comment One very interesting feature is the ability to check the validity of cross-references. @end-comment

tex2xindy recognises all index entries of the form

  \index{...|\macro{where}}


as cross references. Here macro stands for an arbitrary macro name and where is interpreted as the target keyword of the cross references.

If you want to use these cross references with xindy; add the following line to your style file.

  (define-crossref-class "macro")


Additionally, you can assign specific markup to cross references using the markup-crossref-commands.

## 4.15 The keyword mappings don't work as expected!

Sometimes the keyword mappings don't work as expected. Especially in cases with several regular expressions one might get confused about what rule matches exactly when. We have incorporated a detailed logging mechanism that lets one step by step follow the rules that accomplish the keyword mapping.

When running xindy you can turn on this feature with the command line option -L'. This option followed by one of the numbers 1, 2, or 3 turns on the appropriate debugging level. Turning on level 2 or 3 and specifying a log-file with the command line option -l' a trace of the mappings is recorded in the log-file. A sample output looks like the following:

 Mappings: (add (merge-rule :eregexp ^\\bf{(.*)}' \1' :again)). Mappings: (add (merge-rule :eregexp ^\\"([AEOUaeou])' \1')). ... Mappings: (compare \"A\"a' :eregexp ^\\bf{(.*)}') Mappings: (compare \"A\"a' :eregexp ^\\"([AEOUaeou])') match! Mappings: (compare \"a' :eregexp ^\\bf{(.*)}') Mappings: (compare \"a' :eregexp ^\\"([AEOUaeou])') match! Mappings: (merge-mapping \"A\"a') -> Aa'. 

This trace shows that initially two regular expression mappings have been added to the rule set. The second section shows how the keyword \"A\"a' is compared to these rules and substitutions are applied as matches are found. In the last line the result of the keyword mapping is reported.

## 4.16 I'm totally confused by the markup scheme!

A very important feature is the ability to trace all markup tags xindy emits in the markup phase. Simply use the command line switch -t or insert the command

 (markup-trace :on) 

into the index style. This informs xindy to emit additional pseudo markup that can be used to understand and debug the markup phase. An example output might look like the following:

 <INDEX:OPEN> <LETTER-GROUP-LIST:OPEN> <LETTER-GROUP:OPEN ["a"]> <INDEXENTRY-LIST:OPEN [0]> <INDEXENTRY:OPEN [0]> <KEYWORD-LIST:OPEN [0]> <KEYWORD:OPEN [0]> ... 

The symbolic tags directly lead one to the command that is responsible for the definition of that markup tag. For example, the tag LETTER-GROUP-LIST:OPEN indicates that the command markup-letter-group-list is responsible for replacing this symbolic tag by a real one. Give it a try if you find yourself confused by your own markup specification.

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