CSS specification levels
In this article I have referred to different levels of CSS specification. For example, the new work on CSS Grid subgrid is in Grid Level 2, while the new features for Media Queries are part of the Media Queries Level 4 specification. These levels refer to the progress of individual specifications through the standardisation process. You may have heard people talk about CSS3, and the modules that we used to refer to as CSS3 were all the modules that contained CSS, which existed in CS2.1 prior to the modularisation of CSS. In CSS2.1 we had one single specification that included everything in CSS. CSS3 marked the move to a more modular process and from this point each part of CSS could move forward at different rates.
Therefore, a specification, which was at level 3 at that point and became a W3C Recommendation at Level 3, will have new features added to a Level 4. Once that specification is complete then work will start on a Level 5. New specifications such as CSS Grid Layout, which did not exist in CSS2.1, start life at Level 1. A draft goes through various statuses before becoming a W3C Recommendation. Importantly to us as web developers, to get to that point each feature needs to have two different implementations. This prevents CSS being standardised in a way that can only be implemented in one browser. To find out more about how new CSS becomes part of our browsers, watch this talk that I gave at CSSConf.EU: youtube.com/ watch?v=cYGOv2ToZjY.
Above The future of CSS is modular – and that means a change to the way specifications for different features are set out. You can find out more and get involved at w3.org/Style/ CSS/current-work.en.html