[albatross-users] al-values inside al-input

[Gregory Bond]

> * Implement a generic tag class to handle all tags that are not
>   currently Albatross tags.  

> * Inside Albatross tags we would implement functionality which
>   processes any attribute which is prefixed by 'al-' as a Python
>   expression.

Whoa, that's much more ambitious than I had in mind.... and it would probably
change the way things are done with albatross templates quite dramatically. I 
fear for backwards compatibility in this case.

I was considering something a bit more modest:

 - Each al- tag class already knows what attributes they are interested in.

 - The tag classes use has_attrib() and get_attrib() to access them

 - These two functions (and others like write_attribs_except()) can be changed 
   to look up "foo", and if that doesn't exist, look up & evaluate "fooexpr".

 - This could be pretty much backward compatible to applications, tho the tag 
   classes would need a bit of work.  Leave alone the expr attributes 
   (al-value et al), remove the special case handling of nameexpr, valueexpr 
   etc (lots of places) and let the default mechanism kick in.

Greg.