Damian Conway wrote:
[No, I'm not back; I'm just passing by. But I feel that I need to comment on this whole issue]

Thanks! This message has lots of useful information that I would have otherwise probably missed.

It seems that the basic premise of the POD document object model gels well with that early design document, so I look forward to being able to flesh out the details.

Using ^=\s to delimit a line starting with a = will interfere with the Kwid method of:

 = Heading


Which I was imagining would be converted to a DOM tree that when represented in the "Normative XML" would look like:


That's sort of DocBook style, and in fact I was thinking that for the internal representation, DocBook node names could be used where there is no other better alternative. Of course, non-documentation things like Test fragments or inclusions of external entities, like UML diagrams won't have a representation in DocBook :-).

The uses of a leading = in a paragraph are fairly uncommon. For instance, when quoting POD you would simply indent it a bit to make it verbatim and there is no issue.

I see a middle ground; that is, `=` quoting is only is allowed if it directly follows the initial POD marker;

 =head1 Foo
 = =head1
 = =
 = = =head1 That's just getting ridiculous

Which I see as represented by;

 = =head1 That's just getting ridiculous</para>

Which of course would lose the ='s. But that's OK, because if you wanted verbatim you could have just indented the block.

If you wanted to lead a normal paragraph with it, you'd just use the normally implicit =para (equivalent to =pod):

 = = This is what a Kwid =head1 looks like

As for going with =kwid to denote the starting of kwid, I have so far been pessimistically assuming that something like `=dialect kwid`, or `=use kwid` (as described in the design doc you attached) would be required. However, we could allow `=unknown`, where `unknown` is an unknown keyword, to try to load Pod::Dialect::unknown, and hope like hell it provides the Role of Pod::Dialect.

While the `^=` escaping is “active”, the presence or absence of whitespace following the initial `=` will delimit breaks in paragraphs. This has to be so, otherwise the previous example would have been:


 = =head1 That's just getting ridiculous

Which is just plain silly. This follows what people are used to with POD - blank lines must be empty, not just no non-whitespace characters (an increasingly vague concept these days).

So, the POD processing happens in 3 levels (note: the first isn't really mentioned in perlpodspec.kwid, which is a bug);

- chunkification from the original source, into POD paragraphs, which may or may not include an initial `^=foo` marker. At *this* level, the only escaping that happens is the `^=` escaping.

That's all that needs to happen while the code is being read, and for most code that is how the POD will remain, in memory, somewhere intermingled with the Parse Tree for the code, so that the code can still be spat back out by the P6 equivalent of `B::Deparse`

- parsing of these raw chunks into a real POD DOM. Please, tired XML veterans, please don't get upset by the use of the term "DOM", I think the last thing anyone wants is to have studlyCaps functions like `getElementById` and `createTextNode`. It is the tree concept itself which is important, and this pre-dates XML anyway.

Strictly speaking, this step actually converts POD paragraph chunk events into POD DOM events. These can be used to build a real DOM, for instance if you need to do an XPath style query for a link (I was amazed that someone's actually gone and built Pod::XPath!), or they might simply be passed onto the next stage by an output processor with no intermediate tree being built.

So, at this point, dialects get hooks to perform custom mutation of POD paragraph events into DOM events, and the arbitrator of this process ensures that the output events are well "balanced" by spitting out closing tags where it has to. They can store state in their parser object, but none of this state will be preserved past the parsing state.
However, the nodes that they "spit out" after this point may still not be "core" POD, such as for includes or out-of-band objects. These hooks will be sufficient to allow them to hijack subsequent chunks that would otherwise be served to other dialects, ie, they can choose to "arbitrate" subsequent chunks.

I'm aiming to make it so that it is possible for dialects to be "round trip safe", by being able to go back from this DOM state to the original POD paragraph chunks. This would require dialects to "play nice" of course, but is a potential option to help make things like smart text editors be able to automatically syntax highlight POD dialects :).

Linking will be in terms of this intermediate tree, so you won't be able to link to included portions of manual pages :). I'm not sure whether that matters.

- "output ready" form may also either be a stream of events or a DOM tree. In this mode, all of the events from the first stage are simply fed through a loopback preprocessor, which asks Dialects to convert their non-core nodes to core nodes, or drop them, or whatever. At this point, the structure can have handles to out of band objects like images, etc - that can't be converted to XML. Again, dialects are capable of arbitrating the loopback process for any events that *follow* theirs.

Of course, documents that are not in a dialect (and do not have nodes that `=include` and suchlike) will not need any pre-processing to be ready for “output”.

=end list

If there is anything that you think is ghastly wrong with the above picture, let me know of course, but I don't think it's actually all that much different from what has to go on under the hood in a Pod parser or markup tool, anyway. In particular, MarkOv - as the author of the most comprehensive POD markup system there is, this means you! :-)

There is a big question about inline styles still open, and how converting paragraph bodies to a series of POD events works (clearly, this is essential for single-paragraph Kwid list blocks, etc) - but I'm hoping the answer will just smack me in the face as I start to work with ingy on the prototype implementation, and specifying the details of what node types the POD DOM and/or DTD allows.

Now, I've done plenty of planning for this now, it's even looking hopeful! So time for me to keep quiet until I've built something :-).


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