In "'All files and folders' File Type", Context Menu, I have "Rotate Thumbnail: properties rotate=menu". I have tried to read, in the pdf manual, what this menu item does, but I cannot find that under "Raw Commands – Properties", there is any "rotate". Can someone clarify this for me?
The command will, amazingly enough, produce a menu of options that let you rotate the selected thumbnail. (The options being 270 degrees, 180 degrees, 90 degrees and Reset.)
The command only affects the way the thumbnail is displayed and does not modify the actual image file in any way. That can be confusing since the image looks one way in the thumbnail view but is different when you display it in another program... These days Opus can rotate and re-save the image files themselves (via the Image command) for the common image formats so this old function might be considered obsolete (although it does still have a purpose in a few situations).
Perhaps GPSoftware consider it obsolete and have deprecated it, by hiding it from the command editor and manual, to discourage people from using it, but they've left support for it in to avoid breaking people's old configurations that might use the command. Or maybe it's just hidden by mistake; I don't know for sure.