[z3-five] Override it ! (zcml configuration)

[Martijn Faassen]

Georges Racinet wrote:
[snip]
> Of course, it's still possible to write a custom etc/site.zcml for  each 
> given site, but this approach isn't modular enough for the scope  of 
> uses a bundle like CPS has, imho: you don't want to explain a guy  who 
> just wants to override a stylesheet and is writing its first zcml  that 
> he has to dig into the big tentacular site.zcml.

Note that there's another mechanism for customization in Zope 3 that may 
be appropriate for some of the override usecases: layers and skins.

If you want someone to have the ability to override a stylesheet, and 
that stylesheet is in a layer, you could suggest that person to make a 
new product, with a configure ZCML. That configure.zcml should:

* probably include the CPS configure.zcml directly to make sure that 
gets loaded first using <include package=".." />

* define a new layer (1 zcml statement)

* add a ZCML directive for the css resource or ZCML template and the like

* put it in a skin.

And then there needs to be, somehow (this is the part you need to think 
about) a way to tell CPS to use the new skin.

 > Since it's been a while since I've stepped on these problems, I had
 > time to grow some ideas of my own, but I'm curious to hear what Five 
  > devs would say.

I appreciate the analysis and points, both of Zope 3 and the Zope 2 
requirements. We deliberately kept the overriding infrastructure simple 
but I can see it's showing its limits.

I suspect that the same applies to Zope 3 itself, not just Five. The 
problem you describe with deployment, where a product wants to override 
another one, also exists for Zope 3 extensions, right? (if you don't 
want messy site.zcmls that people want to edit; something I don't much 
like either). It may therefore be useful to make this debate into a Zope 
3 core one as well.

As a side-note, I'm also interested in through the web customization 
possibilities for Zope 3 and Five -- the ability to put a new version of 
a ZPT in the ZODB instead of on the filesystem, and have the system use 
that one if it's there.

I'm looking forward to seeing your ideas!

Regards,

Martijn