I have to admit that I am reading this spec thinking about rounded display (aka. watch) and this probably requires brainstorms instead of this nitpicking, but whatever.
The current spec seems to leave screen.orientation.lock("landscape") undefined for the case when the screen width and height are equal because the steps of "update the orientation information" make "current orientation type" always "portrait-primary" or "portrait-secondary" for such case: # 2. Otherwise, if the screen width is less than or equal to the # screen height, set the document's current orientation type to # portrait-primary or portrait-secondary. ("update the orientation information" step 2) I think we shoud drop "or equal to" here and, if necessary, say something like "for the purpose of this specification, it is assumed that the physical device has unequal width and height. User agent MUST treat one physical side or another as if its greater.", but this is awkward so I think just dropping "or equal to" is fine. Some more editorial comments: In step 1 of "update the orientation information" # 1. If the screen width is greater than the screen height, set the # document's current orientation type to landscape-primary or # landscape-secondary. I had trouble realizing that the "screen width" here is a variable and depends on how viewport is rendered (I had assumed it means "device width", I guess). This probably needs a xref to "screen" in 4. Concepts. Or would it be fine if we just use 'screen.width' and 'screen.height' here? In step 3 of "update the orientation information" # 3. Set the document's current orientation angle to the clockwise # angle in degrees between the orientation of the viewport as it is # drawn and the natural orientation of the device (i.e., the top of # the physical screen). I am still having trouble visualizing what "clockwise angle in degrees between the orientation of the viewport" means and I wonder if it would be easier if this is rephrased using "angle from". A picture here would be the best (perhaps adapted from a DeviceOrientation one?). In step 6 of "lock the orientation" # 6. Otherwise, depending on platform conventions, change how the # viewport is drawn in order to make it match another screen # orientation type. However, it has to be part of orientations. I think we should consider revert this change. Having no MAY (or may) here reads like a must to me, and so it sounds kinda confusing even if there's "depending on platform conventions".  http://dev.w3.org/csswg/css-round-display/  https://github.com/w3c/screen-orientation/commit/824cfee4e9009fd8eb7746a9a70b135f2ce3e896 Cheers, Kenny -- Software Engineer, Shenzhen, BGI