Re: Mallard question - link to figures

[Shaun McCance <shaunm gnome org>]

On Wed, 2010-11-17 at 14:35 +0100, Zoltan Kota wrote:
> Hi,
> 
> We are migrating the documentation of pybliographer into Mallard.
> Thanks for Mario!
> There is one thing that does not seem to work: Is it possible, or will
> it be possible in the future, to make a link to a figure?
> For example:
> 
> -----
> <figure id="figopen">
>    <title>Opening a database</title>
>    <media type="image" mime="image/png" src="figures/open.png">
>    <p>Opening a database</p>
>    </media>
> </figure>
> 
> .... text ....
> 
> see the screenshot <link xref="#figopen" />

It is not possible. Links go to pages or sections, never to
block elements like figures or listings. I know this is very
common in traditional print media, where figures are numbered
by chapter, and cross-reference text like "Figure 3-1" can be
automatically generated. Since there's no natural meaningful 
numbering system in Mallard, link text has to rely on titles
only. And titles are optional on figure.

In print, you refer readers back to earlier figures, and they
switch context and flip some pages. You can't show the image
over and over, because paper costs money. In online media,
the cost of showing the image again is near zero.

In DocBook, you can link to literally anything. It's perfectly
valid to link to a phrase element, for example. The code for
generating cross-reference text for those cases is crazy, and
it would be crazier in Mallard with its provisions for extra
link titles.

Of course, we could explicitly limit linking to formal block
elements, i.e. those that can take a title. And if they don't
have a title, we fall back to the id, rather than trying to
chain up. And we'd probably want link titles.

If we allow linking to block elements, people might expect the
automatic links to work with them. Although, heck, maybe there
are useful automatic linking concepts we could have between
figures or between listings.

Also, it complicates cache file generation. We'd have to put
all those block elements into the cache files. That increases
processing time.

So, in summary, there are (not insurmountable) technical issues
that would have to be addressed. And I don't think the need is
as great as in print. I could be convinced I'm wrong.

Also, I'd be interested in seeing other solutions for reusing
figures and other stuff. Collapsible content, for example. Or
mouseovers. Or light boxes. Or some sort of persistent media
sidebar.

-- 
Shaun McCance
http://syllogist.net/