# Jade - James' DSSSL Engine

## Contents

- What is Jade?
- Copyright
- Getting Jade
- Building Jade
  - Win32
  - Unix
- Using Jade
- Jade Extensions
- Current Jade Limitations
- Backends
  - RTF
  - SGML Flow Object Tree
  - TeX
  - SGML Transformation
- Reading the Jade Sources
- Reporting Bugs in Jade
- Contributing to Jade

## What is Jade?

Jade is an implementation of the DSSSL style language. The current version is 0.9. This should be considered a beta test version.

For general information about DSSSL, see my DSSSL page.

You can discuss Jade and get help from other users on DSSSList, the DSSSL Users' Mailing List. I will announce new versions of Jade on DSSSList. To subscribe send mail to majordomo@mulberrytech.com with "subscribe dssslist" as the body of your message. To subscribe to the digest instead, the body should be "subscribe dssslist-digest". The list is archived.

Jade includes the following components:

- An abstract interface to groves. This is designed to be implementable on top of a database, in addition to simple in-memory implementations.

  The source is in the grove directory.

- An in-memory implementation of this interface built with SP.

  This is multi-threaded (on Win32 only at the moment): the grove can be accessed before it is complete and access to a property of a node will block until that property becomes available. This allows the style engine to produce output before it has read all the document.

  The source is in the spgrove directory.

- A style engine that implements the DSSSL style language. This depends on the grove interface, but not the spgrove implementation of that interface. It depends on SP for the parsing of DSSSL specifications. The style engine relies on a backend to actually do the formatting. The backend interface is designed to accomodate browsers as well as command-line applications, but it does not currently provide interfaces that would allow for editing either of SGML documents or DSSSL specs.

  The source is in the style directory.

- A command-line application, `jade`, that combines the style engine with the spgrove grove interface and four backends:
  - A backend that generates an SGML representation of the flow object tree.
  - A backend that generates RTF. This has been tested with Microsoft Word 97 and Microsoft's free Word Viewer 97. Previous versions were tested with Word 95 and Word Viewer 7.1.
  - A backend that generates TeX. Although the C++ part of this is almost complete, much work remains to be done on writing the TeX macros on which the generated TeX code depends. (This backend was contributed by David Megginson.)
  - A backend that generates SGML. This is used in conjunction with non-standard flow object classes to generate SGML, thus allowing Jade to be used for SGML transformations.

  The source is in the jade directory.

## Jade Copyright

Jade is licensed under the same terms as SP. This imposes almost no restrictions even for commercial use.

If you do use Jade in a commercial product, I would ask you, as a courtesy, to let me know about it and acknowledge the use of Jade.

## Getting Jade

If you're using Windows 95 or Windows NT, then you all you need is in the binary distribution.

Otherwise you will need to build it yourself from source. You need the sources for Jade. This package includes the sources for a compatible version of SP (which may be different from the latest released version of SP).

Create a new directory and then unpack the sources file in this directory. The files in sources zip file use CRLF delimited lines, so use unzip -a to unpack on Unix. On Windows you must use an unzip that preserves long filenames, such as WinZip 6.1. You should also make sure that your unzip preserves the case of filenames; this requires using a `-U` option with some versions of unzip.

## Building Jade

### Win32

Only Microsoft Visual C++ 4.2 is supported. It worked with 4.1 last time I tried, but it's only been tested with 4.2.

Open SP.mak as a makefile and build at least the `lib - UnicodeDebug` and `lib - UnicodeRelease` configurations.

Then open jade.mak as a makefile and build the jade configurations.

With the debug configuration the DLLs and EXEs end up in the lib\UnicodeDebug directory; with the release configuration they end up in the bin directory.

### Unix

Only gcc 2.7.2 is supported (2.6.3 and 2.7.1 may also work; don't use 2.7.0).

If you use gcc 2.7.2 with -O on an x86 processor you must use -fno-strength-reduce. gcc 2.7.2.1 fixes this problem.

Building on Unix is tested irregularly, so be prepared to fix build glitches (typically the fix involves adding some template instantiations).

You'll need a Makefile that supports the `include` directive.

Build with `make -f Makefile.jade`. Note that jade requires an SP compiled with `-DSP_MULTI_BYTE`. If you plan to do any development, also do `make -f Makefile.jade depend`.

## Using Jade

Add the directory containing the jade binary to your path, change directory to the dsssl directory, and do

    jade demo.sgm
    nsgmls -s demo.fot

If everything is working, you shouldn't get any errors.

The system identifier of the document to be processed is specified as an argument to Jade. If this is omitted, standard input will be read.

Jade determines the system identifier for the DSSSL specification as follows:

1. If the `-d` option is specified, it will use the argument as the system identifier.
2. Otherwise, it will look for processing instructions in the prolog of the document. Two kinds of processing instruction are recognized:
   `<?stylesheet href="sysid" type="text/dsssl">`
     The system data of the processing instruction is parsed like an SGML start-tag. It will be parsed using the reference concrete syntax whatever the actual concrete syntax of the document. The name that starts the processing instruction can be either `stylesheet` or `xml-stylesheet`. The processing instruction will be ignored unless the value of the `type` attribute is one of `text/dsssl`, `text/x-dsssl`, `application/dsssl`, or `application/x-dsssl`. The value of `href` attribute is the system identifier of the DSSSL specification.
   `<?dsssl sysid>`
     The system identifier is the portion of the system data of the processing instruction following the initial name and any whitespace.

   Although the processing instruction is only recognized in the prolog, it need not occur in the document entity. For example, it could occur in a DTD. The system identifier will be interpreted relative to where the the processing instruction occurs.

3. Otherwise, it will use the system identifier of the document with any extension changed to `.dsl`.

A DSSSL specification document can contain more than one style-specification. If the system identifier of the DSSSL specification is followed by `#id`, then jade will use the style-specification whose unique identifier is `id`. This is allowed both with the `-d` option and with the processing instructions.

The DSSSL specification must be an SGML document conforming to the DSSSL architecture. For an example, see `dsssl/demo.dsl`.

Jade supports the following options in addition to the normal SP options:

`-d dsssl_spec`
  This specifies that `dsssl_spec` is the system identifier of the DSSSL specification to be used.
`-G`
  Debug mode. When an error occurs in the evaluation of an expression, Jade will display a stack trace. Note that this disables tail-call optimization.
`-t output_type`
  `output_type` specifies the type of output as follows:
  `fot`
    An SGML representation of the flow object tree
  `rtf` `rtf-95`
    Microsoft's Rich Text Format. `rtf-95` produces output optimized for Word 95 rather than Word 97.
  `tex`
    TeX
  `sgml`
    SGML (used for SGML-to-SGML transformations)
  `xml`
    XML (used for SGML-to-XML transformations)
`-o output_file`
  Write output to `output_file` instead of the default. The default filename is the name of the last input file with its extension replaced by the name of the type of output. If there is no input filename, then the extension is added onto `jade-out`.
`-V variable`
  This is equivalent to doing

      (define variable #t)

  except that this definition will take priority over any definition of variable in a style-sheet.

Jade ignores the `SP_CHARSET_FIXED` and `SP_SYSTEM_CHARSET` environment variables and always uses Unicode as its internal character set, as if `SP_CHARSET_FIXED` was 1 and `SP_SYSTEM_CHARSET` was unset. Thus only the `SP_ENCODING` environment variable is relevant to Jade's handling of character sets.

## Jade Extensions

The following external procedures are available. These external procedures are defined by a prototype in the same manner as in the standard. To use one of these external procedures, you must make use of the standard `external-procedure` procedure, using a public identifier of `"UNREGISTERED::James Clark//Procedure::name"` where `name` is the name given here, typically by including the following in the DSSSL specification:

    (define name
      (external-procedure "UNREGISTERED::James Clark//Procedure::name"))

Note that `external-procedure` returns `#f` if it doesn't know about the specified public identifier. You can use this to enable your DSSSL specifications to work gracefully with other implementations which do not support these extensions.

### Debugging

    (debug obj)

Generates a message including the value of `obj` and then returns `obj`.

### Simple-page-sequence header/footer control

    (if-first-page sosofo1 sosofo2)

This can be used only in the specification of the value of one of the header/footer characteristics of simple-page-sequence. It returns a sosofo that will display as `sosofo1` if the page is the first page of the simple-page-sequence and as `sosofo2` otherwise.

    (if-front-page sosofo1 sosofo2)

This can be used only in the specification of the value of one of the header/footer characteristics of simple-page-sequence. It returns a sosofo that will display as `sosofo1` if the page is a front (ie recto, odd-numbered) page and as `sosofo2` if it is a back (ie verso, even-numbered) page

### Numbering

    (all-element-number)
    (all-element-number osnl)

This is the same as `element-number` except it counts elements with any generic identifier. If `osnl` is not an element returns #f, otherwise returns 1 plus the number of elements that started before `osnl`. This provides an efficient way of creating a unique identifier for any element in a document.

### External entity access

    (read-entity string)

This returns a string containing the contents of the external entity with system identifier `string`. This should be used only for textual entities (CDATA and SDATA), and not for binary entities (NDATA).

## Current Jade Limitations

This section describes the limitations of the front-end (the general-purpose DSSSL engine): each backend also has its own limitations.

Only the DSSSL Online subset of DSSSL is implemented with the following additions (all part of full DSSSL)

- the math flow objects
- lambda (including #!key)
- let, letrec, let* and named let
- quasiquotation
- node-list-first
- node-list-rest
- node-property
- sgml-parse
- children
- descendants
- attributes
- follow
- preced
- data
- select-elements
- select-by-class
- node-list-no-order
- node-list=?
- node-list?
- node-list
- node-list-map
- node-list-length
- node-list-ref
- node-list-reverse
- named-node-list?
- named-node
- named-node-list-names
- named-node-list-normalize
- process-node-list
- node-list-address (argument restricted to a singletion node-list)
- element-with-id
- empty-node-list

Note that only inherited characteristics that are applicable to some supported flow object can be specified.

Jade supports only a single, fixed grove plan which comprises the following modules:

- baseabs
- prlgabs0
- instabs
- basesds0
- instsds0
- subdcabs

### Character/glyph handling

It only supports a single pre-defined character repertoire. A character name of the form `U-XXXX` where `XXXX` are four upper-case hexadecimal digits, is recognized as referring to the Unicode character with that code. For many characters, it is also possible to use the ISO/IEC 10646 name in lower-case with words separated by hyphens.

Some common SDATA entity names from the ISO entity sets are recognized and mapped to characters. In addition an SDATA entity name of the form `U-XXXX`, where `XXXX` are four upper-case hexadecimal digits, is mapped to the Unicode character with that code.

Jade does not make use of any of the declaration architectural forms related to characters and glyphs.

The following style language declarations (as well as the non-DSSSL Online declarations) are ignored:

    declare-char-characteristic+property
    declare-char-property
    add-char-properties
    define-language
    declare-default-language

### Validation

Several things that it would be desirable to have checked aren't checked:

- When the allowed value of an inherited characteristic is a symbol, jade checks only that the value is a symbol that is allowed as the value of some characteristic; #t and #f are treated as a special kind of symbol in this case.
- Jade doesn't check whether a flow object is occurring in a context where it is allowed.
- Jade does not prevent flow objects being attached to the principal port of a flow object when the flow object shouldn't have a principal port.
- Most type-checking is done at run-time not compile-time.
- Jade does not check for non-inherited characteristics that are required to be specified.
- It doesn't check that optional features that have been used were declared in the features form.

### Other limitations

The following primitives are just stubs:

`char-script-case`
  Always returns last argument.
`char-property`
  Always returns #f or specified default value.
`address-visited?`
  Always returns #f.

## Backends

### RTF backend

Only the following flow object classes are implemented:

`sequence`
`character`
`paragraph`
`paragraph-break`
`line-field`
  Only at the beginning of a paragraph.
`display-group`
`simple-page-sequence`
`score`
  Only type `after` and `through`
`rule`
  Only horizontal orientation. Rules only show up in Page Layout View.
`box`
  Changing indentation inside a box will not work.
`leader`
  The content of the flow object is ignored: a dotted leader will always be used. The specified length is ignored: it always fills out the line.
`external-graphic`
  On Windows platforms, this can be used to embed OLE objects, by making the the value of the `notation-system-id:` a formal system identifier whose storage manager is `CLSID` and whose storage object identifier is the COM CLSID (including surrounding braces). The system identifier may also be just `<CLSID>` (that is, the storage object identifier may be empty); in this case, the OLE default CLSID for the file (usually chosen based on the file's extension) will be used.
`link`
  Only destinations that are single elements in the same RTF output file.
`table`
`table-part`
`table-column`
  The table-auto-width feature isn't properly supported: it's not really possible in RTF.
`table-row`
`table-cell`
`table-border`
math flow objects
  These are converted into Word EQ fields. The Word EQ feature is not powerful enough to do a really good job. The mark flow object class is particularily problematic, because there is no way automatically to compute an appropriate position for the contents of the over-mark and under-mark areas; however, some additional characteristics are provided that allow the positioning to be explicitly specified.

Many DSSSL characteristics cannot be implemented in RTF. The backend does the best it can.

In order to get correct page numbers in Microsoft Word, type the following after opening the document:

1. CTRL+END
2. CTRL+A
3. F9

In Word Viewer 97, you must instead do:

1. CTRL+END
2. ALT
3. V
4. N
5. ALT
6. V
7. P

Page numbers also get updated automatically when you print.

The RTF backend supports some additional characteristics. To use a characteristic named here as `C`, declare it using `declare-characteristic` with the public identifier:

    "UNREGISTERED::James Clark//Characteristic::C"

`heading-level`
  Value is an integer. It applies to paragraph flow objects. If the value is between 1 and 9, then the paragraph is output as a header of this level, otherwise it is output as body text. Using this characteristic allows Word to provide useful outline views and a document map. (Note that Word's handling of document maps for RTF documents is buggy: if you load an RTF document, and the previous document was using the Online Layout view, then RTF will attempt to guess what paragraphs are headings, which it will almost always do wrong. To avoid this, switch to the Normal view before loading an RTF document.) The initial value is `0`
`page-number-format`
  Value is a string as for format-number procedure. This controls the format of the number used by page-number-sosofo and current-page-number-sosofo for references to pages in the simple-page-sequence. The initial value is `"1"`. It applies to simple-page-sequence flow objects.
`page-number-restart?`
  Value is a boolean. If true, then for the purposes of page-number-sosofo and current-page-number-sosofo, the page numbers for this simple-page-sequence will restart from 1. The initial value is `#f`. It applies to simple-page-sequence flow objects.
`page-n-columns`
  Value is a strictly positive integer, specifying the number of columns. The initial value is 1. It applies to simple-page-sequence flow objects.
`page-column-sep`
  Value is a length, specifying the separation between columns. The initial value is `.5in`. It applies to simple-page-sequence flow objects.
`page-balance-columns?`
  Value is a boolean. If true, the columns on the final page of the page-sequence should be balanced. The initial value is `#f`. It applies to simple-page-sequence flow objects.
`superscript-height`
  Value is a length. Specifies the height of the baseline of a superscript above its parent's baseline. It applies to superscript and script flow objects.
`subscript-depth`
  Value is a length. Specifies the depth of the baseline of a subscript below its parent's baseline. It applies to subscript and script flow objects.
`over-mark-height`
  Value is a length. Specifies the height of the baseline of the contents of the over-mark area of a mark flow object above the baseline of the contents of the main area. It also controls the height of the contents of the mid-sup area of the script flow object. It applies to mark and script flow objects.
`under-mark-depth`
  Value is a length. Specifies the depth of the baseline of the contents of the under-mark area of a mark flow object below the baseline of the contents of the main area. It also controls the depth of the contents of the mid-sub area of the script flow object. It applies to mark and script flow objects.
`grid-row-sep`
  Value is a length. Specifies the separation between rows of a grid flow object.
`grid-column-sep`
  Value is a length. Specifies the separation between columns of a grid flow object.

### SGML Flow Object Tree backend

The DTD for the SGML generated is in `jade/fot.dtd`.

Characteristics declared with `declare-characteristic` are not reported.

Flow objects of classes declared with `declare-flow-object` are not reported.

## Reading the Jade Sources

Start with the following headers:

    grove/Node.h
    style/FOTBuilder.h
    style/StyleEngine.h

## Reporting Bugs in Jade

If you find a bug in Jade, please take the time to report it. If Jade crashes on any input whatever, that's a bug and I want to hear about it. If Jade fails to process a specification that conforms to the DSSSL standard in the manner required by the DSSSL standard in a way that is not documented here as a current limitation nor is documented as an error in the proposed Technical Corrigendum to the DSSSL standard, that's a bug and I want to hear about it.

Please report bugs by email to me, `jjc@jclark.com`. Do not post them to comp.text.sgml nor to the sp-prog list.

I do not want to get bug reports about documented limitations, so please read the list of limitations carefully. However, feel free to let me know which of the current limitations you would most like to see addressed.

I also at this stage do not want to hear about bugs in your C++ compiler that prevent it from compiling Jade: if your compiler refuses to compile Jade, I want to hear about it only if

- it is because the Jade source code fails to conform to the current ANSI C++ draft in some way, or
- you have a clean, simple and portable workaround for your compiler's bug.

Before reporting a bug, please check that your snapshot is current.

The most important thing in reporting a bug is to include a complete set of files on which I can run jade and reproduce the problem. Also tell me what command line I should use, and what is incorrect about the behaviour of jade. If the files are large package them up as a tar or zip file and upload them to ftp://ftp.jclark.com/incoming.

It is useful if you have a fix for a bug, but please don't delay sending in the bug while you work on a fix and don't send in a fix without giving me the files to reproduce the bug it fixes.

## Contributing to Jade

Here are some ways you can contribute to Jade:

- Send in good bug reports.
- Write DSSSL style sheets for popular DTDs. People are already working on style sheets for HTML, TEI and Docbook.
- Write another backend. I would like to see the following backends:
  - MIF
  - groff/troff
  - a formatter that can produce output using
    - PDF
    - Windows GDI
    - Plain text
- Write some more documentation.
- Create a test suite.