[Zope-CMF] proposal for cmf:indexable directive

[whit]

here is a sketch of how a working "indexable" configuration would look. 
  Names subject to improvement.

------------

<configure xmlns="http://namespaces.zope.org/cmf"
            xmlns="http://namespaces.zope.org/zope">

  <adapter
   name="SearchableText"
   for="IContent"
   provides="IIndexable"
   factory="SearchableTextExtractor"
   />

  <adapter
   name="folder_order"
   for="IContent"
   provides="ICatalogMetadata"
   factory="folderOrderCalculator"
  />

  <cmf:indexable
   for="IContent"
   attributes='SearchableText
               path
               folder_order'
   metadata='folder_order' />

  <!-- or this for interface lovers --/>

  <cmf:indexable
   for="IContent"
   attributes='IContentIndexableAttrs'
   metadata='IContentMetadataAttrs' />

</configure>

-------------

Our primary goal was is to be able to catalog non-direct
attributes as both indexes and metadata.  This straight forward to 
accomplish.

Eventually, I think it makes sense, as content gets happily dumber, that 
all indexing should work this way.

For backward compatibility, a default adapter could return direct attrs 
from an object for indexing.

  <adapter
   provides="IDefaultIndexable, IDefaultMetadata"
   for="*"
   factory="directAttrAccess"
  />

  <cmf:indexable
   for="*"
   attributes='*'
   metadata='*' />

Ultimately, if you didn't need back compatibility, you could override 
like this:

  <cmf:indexable
   for="*"
   attributes='None'
   metadata='None' />

then developers could determine class by class and interface by 
interface (and perhaps even by event) what was called when an object is 
indexed, thus lowering the overhead of cataloging.

Some other niceties come to mind when thinking about this that may not 
be inially easily attainable; the main two are installation of indexes 
via configuration and the validation of index existence by the 
cmf:indexable handler.

I look forward to y'alls comments.

-w