As announced at the last regular conference call, on Thursday of last week there was a special session of the WG to discuss the use of prefixed property names in our CSS profile. While certain proposals were rejected and some aspects of others were agreed to, we were unable to achieve consensus for a final recommendation. We have narrowed the field to the following two recommendations:
1. Authors should/must include both prefixed and unprefixed versions of properties in their style sheets. Reading systems that implement these properties must support the prefixed versions. We will mandate that the unprefixed version come either before or after the prefixed one, with clarifying text about aliasing the properties. This allows us to drop prefixes in the future, since content should continue to work. It also allows epub content documents to work unmodified in browsers once the CSS specs are implemented without prefixes in those user agents.
2. All properties from pre-CR CSS modules must be prefixed. Unprefixed properties should not/must not be included. Reading systems that implement these properties must support the prefixed properties. This simplifies style sheet creation, but requires reading systems to maintain prefix support for the foreseeable future. Proponents of this approach argue that is the case anyway, and having a simple rule like this is easier for content creators.
While we did not come to consensus on either solution, I don't think there were "can't live with" positions for either. In addition, there was consensus that we would reference dated drafts for the syntax of these properties, while allowing the semantics to be defined by the current published draft. We do need to decide what "published draft" means, so there is no ambiguity (e.g. do we disallow editors drafts?). We will monitor the status of drafts until July, dropping prefixes if possible as some modules may hit CR before our final release. We will also coordinate with the CSS WG to make sure drafts we reference for syntax are roughly up-to-date.