I noticed in the live demo and documentation screenshots that, in relation to image accessibility, the word "description" is used when referring to image "alternative text":

This image is missing a description

If this image is important (i.e. it's not a little design flourish), then add a description of this image by clicking the image in the editor and then the image button and editing the description. If this image is not important, then leave the description blank so users who can not see the image will be able to enjoy this page.

Is there a reason for this? Granted fewer novice users will understand "alternative" text but I think there's a usability issue if they look to enter text in a "description" field of the image properties dialog that doesn't exist (it reads "alternative text").