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Plone Theming or: How I Learned to Stop Worrying and Love collective.xdv

Recently I’ve been tasked with looking at how we can improve our Plone theming process.

One of the problems that most teams come across on any web project is how to spend less time doing the basics and more time solving the unique problems that each project throws up. This seems to be especially true when it comes to skinning / implementing user interfaces. No matter what framework / CMS I’ve used (and I’ve used plenty) it’s often hard to square the circle between what we want as output and what is actually produced.

Another aspect that can eat up time is having to implement user interface changes during development. Even with the best sign-off procedures, designs, and by extension HTML templates are often subject to change. With that in mind the key objectives we are looking for in a theming method are:

  • easily portable between projects.
  • full control over CSS/HTML and JS output.
  • working in parallel with the development team.

So lets look at the various theming options for Plone.

“Plone theming is getting a bit complicated”

You’re not wrong. From what I can see you have 2 options:

  1. Write a custom stylesheet. It’s amazing what you can do with CSS, but that alone won’t cut it. We need to able to specify the HTML output to meet our high standards of accessibility and design.
  2. Create a ‘vanilla’ theme product. Creating a Plone theme is not for the faint hearted and to be honest it had me stumped. You really need to have a solid understanding of Plone and Zope to create anything worthwhile and while that is not necessarily a problem it’s certainly not my area of expertise.

I could probably grab some developer time here at Isotoma to help me put together this ‘vanillla’ product, but even that doesn’t answer our needs in the level of flexibility we require. There must be an easier way….

Deliverance / Collective.xdv

The future of Plone theming lies in Deliverance / Collective.xdv and will be at the core of Plone 4 theming (so I’m told). You can start using it now though. (see this excellent tutorial to get started )

It took a little effort to get a working buildout, mainly because I couldn’t get lxml working on my mac (necessary for collective.xdv). So I installed it on an Ubuntu VM which worked just fine.

Once I’d got it working it didn’t take me long to realise the potential of this new way of theming. In a nutshell, it allows you to have whatever output you want. Not only that but it allows template development to happen separately and in tandem with the main development effort.

Let’s have a quick look at how it works. At it’s simplest level you have 2 files: theme.html and rules.xml. The theme.html file is a standard html template and you can write this however you want. It is the rules file where it gets interesting. I won’t go in to the full details (see here for a full description) but here are some examples of what you can do.

Replace content:

<replace content='//*[@id=”content”]' theme='//*[@id=”content-area”]' />

this replaces the element in the theme.html with whatever content Plone produces within #content element.

Append / prepend content:

<append content='/html/head/style' theme='/html/head' />

this adds all the styles from Plone.

Discard content:

<drop theme='/html/head/comment()' />

This removes comments form the theme.html appearing in the site.

It uses Xpath, something that I’m familiar with and very easy to learn. With deliverance it gets even easier because you can use CSS 3 selectors. All-in-all you have a very powerful way of theming Plone whilst having a fantastic level of separation and flexibility.

I’m very hopeful that collective.xdv / Deliverance will be the solution we are looking for and I’m really looking forward to using it on forth coming projects.