I apologize that this issue has not been fixed yet. It has now been fixed and the update will go live with the next documentation update. As a side note, we have recently released public GitHub repository of our documentation, which could be modified by everyone. And as pointed in the blog post
on that topic "all valuable contributions will be rewarded with Telerik points–just make sure you are using the same email for your GitHub and Telerik.com accounts."
As for the first question posed, I guess that the first one comes after comparing the RadPageLayout breakpoints and the RadDeviceDetectionFramework ranges. The RadPageLayout has different viewport breakpoints than the ones used for RadDeviceDetectionFramework due to its different purpose. The RadPageLayout is used for setting up layout, not for enabling render mode. Thus, it needs one more level for enabling different layout for different cases. In addition, the RadDeviceDetectionFramework provides the opportunity to define your own custom ranges, if the default ones does not fit your case. That is why there is no ExtraSmallScreenSizeRange for RadDeviceDetectionFramework.
And for your second question, the answer is that you cannot set a range with open top end. You could define it with a greater number as a top border, but it cannot be empty.
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