page-sequence-master spec questions

[Kelly Campbell <ca...@camk.net>]

I've been trying to study the xsl spec in regards to helping Arved with 
the flow/static content regions implementation, and I think I sort of 
understand what the spec is saying. I just wanted to solicit some feedback 
from Arved or anyone else on the list who has studied this to make sure 
I'm understanding it, and also to see if anyone has some good examples of 
where this would be used in publishing, say, a book.

The rest of this message might be alot to digest. If anyone has pointers
to examples, tutorials, or other resources that might make this clearer to
me, I'd appreciate it. I think I understand the static content pretty well
since it is rather straightforward. It's the flows and how they relate to
named regions that I'm struggling with.

I tried to rewrite the spec of page-sequence-master in normal human 
readable terms. My brain can only handle so many sequences of words with 
the word "sequence". Here's what I gleaned:

>>>>> BEGIN

6.4.7: fo:page-sequence-master

There are 2 kinds of sub-sequences:
 1. a list of references to page masters
 2. a repeating list of page masters

Constraint: 

The children of the fo:page-sequence-master make a list of
"sub-sequence-specifiers"

properties of this constraint:

a) the resulting page sequence can be grouped into lists of pages which
   map 1:1 to the list of sub-sequence-specifiers which are children of 
   the page-sequence-master

b) for each group of pages, the pages satisfy the constraints of the
   cooresponding sub-sequence-specifier

Note: there can be more sub-sequence-specifiers than there are groups of
pages

It is an error if the entire list of sub-sequence-specifiers is used up
and some areas returned by a flow are not placed. Implementations may
recover by reusing the last sub-sequence-specifier that was used to
generate a page.

<<<<< END

Questions: 

On a bounded repeatable-master-reference, is property b) broken if the
flow is longer than the allowed number of repeating pages? 

What do you do with the left-over flow content if b) can't be met?

Of the two types of sub-sequences, I'm assuming you can intermix them. Is 
this correct?

When you have just a list of simple-page-master-references, do you just 
iterate over them, e.g. m1, m2, m3, m1, m2, m3, m1... or does property 1 
not hold if you do this?

When you have a flow that wants to be associated with a named region, e.g. 
xsl-region-body2 in multiflows.fo (Arved's examples), what do you do? 
start the new sub-sequence with the second repeatable-page-master I 
assume. What if the flow wants the default xsl-region-body? which 
sub-sequence do you use? 

Can flows be named for and render into before and after areas just like 
static content?


-Kelly
 -- 
Kelly A. Campbell                        Software Engineer
camk@channelpoint.com                    Channelpoint, Inc.
camk@camk.net  camk@merlotxml.org        Colorado Springs, Co.

Re: page-sequence-master spec questions

[Arved Sandstrom <Ar...@chebucto.ns.ca>]

At 01:18 AM 11/9/00 -0700, Kelly Campbell wrote:

[ Snippage ]

>On a bounded repeatable-master-reference, is property b) broken if the
>flow is longer than the allowed number of repeating pages? 

There are more pages in the sequence than can be mapped to the 
subsequence-specifier; the pages do NOT satisfy the constraints.

>What do you do with the left-over flow content if b) can't be met?

As you suggest, you don't know that there is too much flow for the 
subsequence-specifier, as a rule, until you lay stuff out. At that point I'd 
say the app throws an exception: the FO explicitly set an incorrect 
"maximum-repeats". The process terminates because the FO was wrong.

>Of the two types of sub-sequences, I'm assuming you can intermix them. Is 
>this correct?

I'm not sure I understand. An fo:page-sequence can only reference 1 
simple-page-master OR 1 page-sequence-master. In the sense that one FO file 
can have multiple page-sequences, each referencing either a different 
simple-page-master, or a different page-sequence-master (with each of 
_these_ being a list of references), then yes, at that level. But there is 
no intermixing of masters, directly, for a given page-sequence. Section 6.4.7
indicates that the possible and allowable intermixing is for single and
repeatable _page-master-references_.

>When you have just a list of simple-page-master-references, do you just 
>iterate over them, e.g. m1, m2, m3, m1, m2, m3, m1... or does property 1 
>not hold if you do this?

There are N pages that map to N single-page-master-references. A 
single-page-master-reference is used once and once only. So there is no 
iteration of the sort that you suggest.

I should add that the XSL spec, in Section 6.4.7, allows us (FOP developers) 
to recover from subsequence-specifier exhaustion by using the last one. I 
don't have my code right in front of me (I'm on Windows, and my stuff is on 
Linux), but as I recall, I considered that in most cases this was not 
sensible, particularly for an explicit maximum-repeats situation. If someone 
were to argue that if an FO specified 3 single-page-master-references m1, m2 
and m3, and we needed 5 pages, and since the spec would allow us to re-use 
m3 to layout page 4 and page 5, that we should do it this way, I could be 
swayed, provided that we issued a warning.
  
>When you have a flow that wants to be associated with a named region, e.g. 
>xsl-region-body2 in multiflows.fo (Arved's examples), what do you do? 
>start the new sub-sequence with the second repeatable-page-master I 
>assume. What if the flow wants the default xsl-region-body? which 
>sub-sequence do you use? 

I should elaborate on my take on multiple flows in a page-sequence. The BNF 
in Section 6.4.5 indicates that we have ONE fo:flow. However, bearing in 
mind that the language "flow children" means both fo:flows and 
fo:static-contents, there is at least one revealing phrase elsewhere in that 
section, namely:

"The default ordering constraints apply to the child fo:flow objects; 
special ordering constraints apply to the child fo:static-content objects."

This clearly suggests the presence of multiple fo:flows. Furthermore, 
consider a situation that is probably not out to lunch, where the body 
content of alternating pages (left and right) logically comes from different 
streams.

Having said all that, "multiflows.fo" is a stretch-the-limit "proof of 
concept" FO that explores the spec. It's a test case for fringe behaviour. 
So I'd be careful with it. :-) However, I do believe that in that example, 
as atrocious as it might be, when flow 1 runs out, and the constraints on 
the first repeatable-page-master-reference certainly are not violated, flow 
2 can be satisfied by repeatable-page-master-reference #2, and so forth 
(order must be satisfied). But it's ugly. Much better to use multiple 
page-sequences.

>Can flows be named for and render into before and after areas just like 
>static content?

Yes, and static-content can go into the region-body. We just haven't set up 
FOP that way.

It ought not to be any great stretch to go for broke and adapt FOP to have 
regions (all 5 of them) accept content from _any_ flow.

Arved

Senior Developer
e-plicity.com (www.e-plicity.com)
Halifax, Nova Scotia
"B2B Wireless in Canada's Ocean Playground"