[silva-dev] public rendering flexibility

[Martijn Faassen]

Hi there,

An idea dump about a possible way to make Silva extensible and more
flexible in a new direction: view rendering pipelines.

The current setup of Silva concerning public views uses particular 
widgets which are in the 'widgets' tree to do the public rendering.
Each widget is in effect a view for an XML node. When publically rendering,
a widget is looked up for an XML node by element name (tag name), and this
widget has a 'render' method which gets called. This then is a page template
and/or python script that does the rendering of the widget to HTML.
Public widget take care of the public rendering.

Frequently a particular Silva site manager wants particular elements
to render differently. Often enough CSS is powerful enough to allow
this. This already works for Silva; Silva spits out simple HTML for
documents and it's easy to associate a stylesheet to that.

Sometimes it's not enough; perhaps a local site manager wants the TOC
to really render in a different way. In this case it would be useful
to override a particular element with new rendering code.

This is currently hard. It will take some re-engineering of the widget
and view architecture to accomplish this.

What is easier to accomplish is a simpler approach. This will introduce
more maintenance burden on the site maintainer but it is very flexible.

Imagine there's a service_xml_rendering or something like that. In
it, the site manager can control which rendering pipeline transforms the
XML coming from the Silva Document (or other objects) into HTML.

The default uses the current widget tree to do it. It should also be
easy to plug in different widget registries which may use different widget
trees. Applying the page template in the end here remains the same; only
the public content rendering changes.

This would require maintaining a near-copy of the public widget tree
so it'd be a maintenance burden, but it'd at least be possible.

More powerful flexibility is also possible. Each Silva object knows how
to represent itself as XML. It should be possible to plug in XSLT
transformation sheets to transform this XML into HTML as well, or
basically any mechanism to do this transformation you like.

With XSLT it may be nice to actually disable the whole page template system
(just plug in a minimal macro for public layout perhaps) and let all the
HTML rendering, including navigation, be the responsibility of the 
XSTL template. The requirements for the various sources of XML data
would increase though; the XSLT would also need access to an XML representation
of the folder tree, for instance, in order to render navigation elements.

What do people think? 

Regards,

Martijn