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## Language Versions

### Stable Versions

Since quickbook 1.3 the `quickbook` attribute in the document block selects which version of the language to use. Not all changes to quickbook are implemented using a version switch, it's mainly just the changes that change the way a document is interpreted or would break existing documentation.

#### Quickbook 1.3 and later

- Introduced quickbook language versioning.
- In the documentation info, allow phrase markup in license and purpose attributes.
- Fully qualified section and headers. Subsection names are concatenated to the ID to avoid clashing. Example: `doc_name.sect_name.sub_sect_name.sub_sub_sect_name`.

#### Quickbook 1.5 and later

- Ignore template argument separators inside square brackets.
- Don't separate the final template argument if the `..` separator was used. i.e. never mix `..` and whitespace separators.
- Statically scope templates and their arguments rather than dynamically scope them.
- Give table ids, and let you set them.
- Allow spaces between the `:` character and ids in elements which can have ids.

### Quickbook 1.6

Everything described in here may change depending on the feedback received.

#### Includes with docinfo

In quickbook 1.5 if you include a file which starts with a docinfo block, it's ignored and the file is expanded in place. In quickbook 1.6 it's treated as a document nested in the current position. So if it has an 'article' docinfo block, boostbook 'article' tags are used.

It also mostly generates the same markup as if the file was converted separately - so for example, the same ids are generated, the document is processed using the language version specified in the docinfo block. If no language is specified it uses the default (1.1) not the version of the document that included it. This might seem surprising, but is requried so that quickbook will convert it the same way as if it was converted separately.

So for the most part, includes with a docinfo are like an `xinclude`, apart from a couple of differences. Templates and macros defined in the parent document are used in the included document, and the id generator rewrites ids that clash between multiple documents.

If an included document doesn't have a docinfo block, it's just included as before.

#### Scoping templates and macros

A long standing quickbook bug is that macros are scoped by file, but templates aren't. So you can define templates in a separate file and include them, but not macros. This has been fixed so that templates defined in one file won't 'leak' into another.

But this means there's no way to define templates in a separate file - a useful feature. To do this the `import` element has been adapted to also support quickbook files. If a quickbook file is imported, the templates and macros defined in it are added to the current scope, but nothing else contained in that file is used. This could be used to create template and macro library files. This matches the existing semantics of importing code snippets.

When importing templates, they're bound to the language version of the file they were defined in. This means that if you import them into a file with a different version it won't change the way they're interpreted. Although, as we'll see later, the generated boostbook is slightly different.

#### Including C++ and python files

As `import` now supports quickbook files, `include` also supports source files. It includes any quickbook contained in comments outside of code snippets. Code snippets in the file are available to be expanded within the file but are scoped to the file. In exactly the same manner as when templates and macros are scoped in an included quickbook file.

#### Id Generation

Id generation in quickbook 1.5 is a bit buggy, but that can't be fixed without a version switch as it will break existing documents. For example in quickbook 1.5 when you include a quickbook file, it stops using the explicit id from the documentation info and generates a new id from the document title to use instead.

The id generator in quickbook 1.6 has been improved in some other ways to. When generating ids from section titles, table titles etc. it always uses the quickbook source rather than the generated boostbook to generate the id. It then cleans up the id slightly, trimming leading and trailing underscores and replacing multiple underscores with a single underscore. Then if the newly generated part of the id is longer than 32 characters it truncates it.

While the new id generator generally creates better ids, it's more likely to generate duplicates so quickbook needs to handle duplicates better. When there are multiple identical ids, quickbook chooses one to use based on a priority list - anchors are preferred, then explicit document and section ids, then other explicit ids, followed by the generated ids. Then any other explicit ids in the document have numbers added to avoid duplicates - first the explicit ids in the order they appear and then the generated ids. A generated id which accidentally clashes with an explicit id should never change the explicit id.

Older language versions still generate the same ids they always have, with the exception of duplicate ids which are handled using the new mechanism - this is not a breaking change since duplicate ids can't be linked to.

#### Compatibility Mode

As mentioned before, changing the id generator will break links in documents written using an old language version. So to ease the transition a 'compatibility mode' is used, this just requires an extra attribute in the docinfo, for example if you're converting a 1.5 document to 1.6:

    [article Document
    [quickbook 1.6]
    [compatibility-mode 1.5]
    ]

This means the document will be parsed as 1.6, using all the new features, but ids (and possibly other markup) will generated as they were for a 1.5 document.

Compatibility mode is also implicitly used when generating templates written in a different language version to the current document. So the template is parsed in the version it was written for, but generates boostbook that's compatible with the current document.

#### Version info outside of document info block

Can now use `quickbook` and `compatibility-mode` tags at the beginning of the file. Either before or without a document info block. This is useful for files just containing templates, which don't really need a document info block.

If you don't specify `compatibility-mode`, the behaviour depends on whether or not you have a docinfo block. If you do it uses the file's quickbook version, if you don't it inherits the parent's compatibility mode even if you specify a quickbook version. This is the right thing to do - mixing compatibility modes within documents is problematic. It might actually be a mistake to allow them to specified outside docinfo blocks.

This change is also backdated to older versions. So when including from an older version, the included file's version can be set (older versions ignore document info in included files).

#### Explicit Heading Ids

Headings can now be given explicit ids:

    [heading:id A heading with an explicit id]

#### Punctuation changes

In 1.6, quickbook is more consistent about how it parses punctuation. Escapes are now supported in links, anchors, table titles, image attributes etc. The flip side of this is that quickbook is now stricter about unescaped brackets. They can still be used, but need to match up, otherwise there's an error.

Since quickbook now matches up square brackets it will fix some mis-parses. For example `[*[bold]]` used to parse as [bold] - note that the closing square bracket isn't bold, now it parses as [bold]. In this case it's just a subtle visual difference, but it could cause odd problems, for example when nested in a table cell.

#### Table Titles

Table titles are now parsed as phrases, so some markup is allowd:

    [table [*bold title]]

Which is an empty table with a bold title. The title is no longer ended by a newline, but by either a closing square bracket, or two opening square brackets - which you get at the start of the table cells, so this now works:

    [table Simple[[heading 1][heading 2]][[cell 1][cell 2]]]

#### XML base

A problem when using `xi:include` tags in escaped boostbook is that you typically don't know which directory the boostbook file will be in, so it's impossible to use relative links. This can be fixed by adding an `xml:base` attribute to the document tag. To do this use the new `xmlbase` attribute in your document's docinfo block. For example to make escaped `xi:include`s be relative to the directory of the file:

    [library Library documentation
    [quickbook 1.6]
    [xmlbase .]
    ]

Any paths in `xinclude` elements will be rewritten accordingly. Note that most documents won't need this, and probably shouldn't use it. Only use it if you're totally sure that you will need it.

#### New Elements

New elements in 1.6 (to be documented later):

- `block`
- `ordered_list`
- `itemized_list`
- `role`

#### Pargraphs in lists

I'm still refining this, but paragraphs and block elements can now be used in lists:

    * Para 1

      Para 2
      * Nested Para 1

        Nested Para 2

            Code block
      Para 3

generates:

- Para 1

  Para 2

  - Nested Para 1

    Nested Para 2

      Code block

  Para 3

The docbook markup that this generates is pretty bad, but seems to create okay html.