Extended release notes here[1]  as well as an explanation of the new object system for extending it, <i>ggproto</i>, here[2]<p>[1] <a href="https:&#x2F;&#x2F;github.com&#x2F;hadley&#x2F;ggplot2&#x2F;releases&#x2F;tag&#x2F;v2.0.0" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;hadley&#x2F;ggplot2&#x2F;releases&#x2F;tag&#x2F;v2.0.0</a><p>[2] <a href="https:&#x2F;&#x2F;cran.r-project.org&#x2F;web&#x2F;packages&#x2F;ggplot2&#x2F;vignettes&#x2F;extending-ggplot2.html" rel="nofollow">https:&#x2F;&#x2F;cran.r-project.org&#x2F;web&#x2F;packages&#x2F;ggplot2&#x2F;vignettes&#x2F;ex...</a>