ResponsiveImagesCG/picture-element — pull request #235 by Wilto (2014-08-01 15:50:54+00:00)
Title: Closes #234 - Clarify that percentage-based values are invalid in `sizes`

![image](https://cloud.githubusercontent.com/assets/439942/3781195/9a9ed32e-1993-11e4-838d-8c21f0f96d63.png)