pandoc-lua-filters/README.md

# text-crossrefs: cross-references to arbitrary portions of text in Pandoc

This filter extends Pandoc's cross-referencing abilities
with references to any portion of text
by its page number, its note number (when applicable)
or an arbitrary reference type (with ConTeXt or LaTeX output).
It currently supports the following output formats:

  * context
  * docx
  * latex
  * odt
  * opendocument

## Format-specific preliminary notices

### DOCX and ODT/Opendocument

When opening for the first time a file produced by Pandoc with _text-crossrefs_,
you should have to refresh the fields in order to get the correct values.
In LibreOffice, press `F9`; in Word, a dialog box should appear when the file opens.

### TeX-based formats

All references are wrapped in a macro named `\crossrefenum`.
It has two optional arguments:
the first one is the reference type,
the second indicates whether the prefix (e.g. “p. ”) should be printed or not
(can be set to `withprefix`, `noprefix`, `yes` or `no`).
The default values for these arguments should match
those of `tcrf-default-reftype` and `tcrf-default-prefixref`
(resp. `page` and `yes`, i.e. `withprefix`).
The mandatory argument of `\crossrefenum` is a group enclosing one or more groups.
Each of them contain a reference (either a single reference or a range).

Here are some valid invocations:

  * `\crossrefenum[note][withprefix]{{lblone}{lbltwo}{lblthree}}`
  * `\crossrefenum[page][noprefix]{{lblone}{lbltwo}{lblthree}}`
  * `\crossrefenum[noprefix]{{lblone}{lbltwo}{lblthree}}` (the first argument defaults to `page`)
  * `\crossrefenum{{lblone}{lbltwo}{lblthree}}` (the second argument defaults to `withprefix`)
  * `\crossrefenum{{only-one}}` (even if the enumeration is limited to one item, it must be in a group)
  * `\crossrefenum{{lblone to lbltwo}{lblthree}}` (the first reference points to a range)

It is up to you to define `\crossrefenum` in your preamble.
If your target format is LaTeX, it should be possible to define it as a wrapper
for the `\zcref` macro provided by [the zref-clever package](https://ctan.org/pkg/zref-clever).
Alternatively, you can use [my implementation](TODO),
which currently supports ConTeXt and LaTeX.
Here are some hints about the implementation of the `\crossrefenum` macro:

  * [The `\crossrefenum` macro is supposed to output non only the numbers,
    but also the prefixes and delimiters (e.g. “p. ” and “–”)]{#prefixes-tex};
  * In ConTeXt, there is no way to retrieve the note number
    from a `\reference` or a `\pagereference` contained in the note
    as one would from a `\label` in LaTeX.
    To work around this, footnotes are labelled automatically with `note:`
    followed by the first identifier attached to a span in the note.
    Contrary to the ConTeXt syntax, this label is placed _after_ the footnote content,
    so the `\footnote` macro has to be redefined.
    If your template includes the `header-includes` metadata variable like the default one does,
    this redefinition will happen automatically.
    Otherwise, you can copy-paste the following code in your preamble:

    ``` {=tex}
    \catcode`\@=11
    \let\origfootnote\footnote
    \def\footnote#1#2{
      \def\crfnm@secondArg{#2}%
      \ifx\crfnm@secondArg\crfnm@bracket
        \def\crfnm@todo{\crfnm@footnote@withlabel{#1}#2} %
      \else
        \def\crfnm@todo{\origfootnote{#1}#2}%
      \fi
      \crfnm@todo
    }
    \def\crfnm@bracket{[}
    \def\crfnm@footnote@withlabel#1[#2]{\origfootnote[#2]{#1}}
    \catcode`\@=13
    
    ```

## Usage

### Basics

Mark the span of text you want to refer to later
with an identifier composed of alphanumeric characters, periods, colons, underscores or hyphens:

``` markdown
Émile Gaboriau published [_L'Affaire Lerouge_ in
1866]{#publication}.[^1]

[^1]: It is a very [fine piece of literature]{#my-evaluation}.

[It was very popular.]{#reception}
```

To refer to it, write another span with class `tcrf` containing the target's identifier.
If the span you are referring to is part of a footnote,
you can refer to it either by page or note number
according to the value of the `reftype` attribute (defaults to `page`).
For instance, this:

``` markdown
See [publication]{.tcrf} for the publication date. I gave my
opinion in [my-evaluation]{.tcrf reftype=note}, [my-evaluation]{.tcrf}.
```

will render in ConTeXt or LaTeX output:

``` tex
See \crossrefenum{{publication}} for the publication date. I expressed
my thoughts about it in \crossrefenum[note]{{my-evaluation}},
\crossrefenum{{my-evaluation}}.
```

If you want to give a reference by note _and_ page number like in the example above,
you can also use the following shorthand:

```md
[my-evaluation]{.tcrf reftype=pagenote}
```

In fact, you can use any identifier, including those automatically set by Pandoc.

To suppress the prefixes (e.g. “p. ”), you can set the `prefixref` attribute to `no` (defaults to `yes`).
It can be useful, for instance, for small manually formatted indexes[^comma-syntax]:

``` markdown
Gaboriau: [publication, my-evaluation, reception]{.tcrf prefixref=no}
```

[^comma-syntax]: About the comma-delimited syntax used in this example, see [the section on enumerations below](#enums).

### Page ranges

You can refer to a page range like this:

``` markdown
If you want to know more about _L'Affaire Lerouge_, see [publication>reception]{.tcrf}.
```

The separator (here `>`) can be set to any string of characters
other than alphanumeric, period, colon, underscore, hyphen and space
(see the [customization options](#common-opts)).

In LaTeX and ConTeXt output, the above-mentionned `\crossrefenum` macro
should be defined so that the range is printed as a simple page reference if the page numbers are identical.
The syntax of a range is[^customize-range-tex]:

``` tex
\crossrefenum{{publication to reception}}
```

[^customize-range-tex]: Note that [it can be customized](#tex-options).

In DOCX and ODT/Opendocument output,
a range will be printed as a range even if the numbers are identical.

### Enumerations {#enums}

You can enumerate several references as a comma-delimited list, for instance:

``` markdown
[ref-one, ref-two>ref-three, ref-four]{.tcrf}
```

In DOCX and ODT/Opendocument output, all these references will be printed,
potentially resulting in unnecessary repetitions.
In TeX-based output formats, they will be wrapped in `\crossrefenum` like this
and should be collapsed by the macro when it is desirable:

``` tex
\crossrefenum{{ref-one}{ref-two to ref-three}{ref-four}}
```

## Customization

### Common options {#common-opts}

The following metadata fields can be set as strings:

  * `tcrf-references-enum-separator`:
    * the string between two references in an enumeration in a reference span;
    * defaults to a comma followed by a space.
  * `tcrf-references-range-separator`:
    * the string used to separate two references in a reference span;
    * defaults to `>`.
  * `tcrf-only-explicit-labels`:
    * set it to `true` if you want _crossrefenum_ to refer to spans with class `label` only;
    * defaults to `false`.
  * `tcrf-default-prefixref`:
    * default value for the `prefixref` attribute;
    * defaults to `yes`.
  * `tcrf-default-reftype`:
    * default value for the `reftype` attribute;
    * defaults to `page`.

### Options specific to DOCX and ODT/Opendocument

Here are some metadata fields for the `docx`, `odt` and `opendocument` formats only
(see [above](#prefixes-tex) why they are ignored in ConTeXt and LaTeX output):

  * `tcrf-page-prefix`: 
    * “page” prefix; 
    * defaults to `p. `.
  * `tcrf-pages-prefix`: 
    * “pages” prefix;
    * defaults to `pp. `.
  * `tcrf-note-prefix`: 
    * “note” prefix;
    * defaults to `n. `.
  * `tcrf-notes-prefix`: 
    * “notes” prefix;
    * defaults to `nn. `.
  * `tcrf-pagenote-separator`:
    * the separator between the enumerated references in the output file
      when `reftype` is set to `pagenote`;
    * defaults to a comma followed by a space.
  * `tcrf-pagenote-at-end`:
    * the string printed at the end of a `pagenote` reference in the output file;
    * defaults to the empty string, but it can be used to achieve something like *n. 3 (p. 5)*
      (see the sample file).
  * `tcrf-pagenote-factorize-first-prefix-in-enum`:
    * defines if the prefixes of the type printed first in a reference to page and note
      should be repeated (like in “p. 6, n. 1 and p. 9, n. 3”)
      or set globally at the beginning of the enumeration (like in “pp. 6, n. 1 and 9, n. 3”);
    * defaults to `no`, can be set to `yes`.
  * `tcrf-pagenote-first-type`:
    * the type of the reference number that is printed first in references to page and note;
    * defaults to `page`, can be set to `note`.
  * `tcrf-range-separator`:
    * the string separating the page numbers in a range;
    * defaults to `–`.
  * `tcrf-references-enum-separator`:
    * the string separating the elements of an enumeration in a reference span;
    * defaults to a comma followed by a space.
  * `tcrf-multiple-delimiter`:
    * the string between two elements (but the two last ones) in an enumeration;
    * defaults to a comma followed by a space.
  * `tcrf-multiple-before-last`:
    * the string inserted between the two last elements in an enumeration;
    * defaults to `and` surrounded with spaces.

### Options specific to the formats based on TeX {#tex-options}

Since TeX is extensible, you may wish to support types
other than `page`, `note` and `pagenote` for ConTeXt and LaTeX output.
`tcrf-additional-types` can be provided with a list of supplementary accepted types, e.g.:

``` yaml
tcrf-additional-types:
- line
- figure
```

Once declared, these types can be used as the value of `reftype`
in the same way as `page`, `note` and `pagenote`.

In addition, the following metadata field can be used to control the rendering of ranges of labels in `\crossrefenum`:

  * `tcrf-range-delim-crossrefenum`:
    * the delimiter between the labels of a range in the TeX output file;
    * defaults to `to` surrounded with spaces.

## Compatibility with other filters

_text-crossrefs_ must be run after all filters that may create, delete or move footnotes, such as citeproc.

In a citation inside square brackets, the span bearing an identifier should not include
a citation key, a locator or a `;` delimiter.
When it follows immediatly the locator,
you should protect the locator with curly brackets.
For example, this should work:
 
 ``` markdown
 [@Jones1973, p. 5-70; @Doe2004[]{#jones-doe}]
 
 [@Jones1973, p. 5-70; [it was elaborated upon]{#further-elaboration} by @Doe2004]
 
 [@Jones1973, {p. 5-70}[]{#ref-to-jones}; @Doe2004]
 ```
 
not that:
 
 ``` markdown
 [[@Jones1973, p. 5-70]{#ref-to-jones}; @Doe2004]
 
 [[@Jones1973, p. 5-70; @Doe2004]{#jones-doe}]
 
 [@Jones1973, p. 5-70[]{#ref-to-jones}; @Doe2004]
 ```