disappearing View option …

… or, "Now you see it, now you don't." Pending the arrival of my nice new TCS, I thought I'd remind myself of how out-of-the-box FM12 displays DITA files. Opened a .ditamap no problem, fairly familiar-looking tree view. Explored. Found a View menu, with two options Structure view … and Document view … Clicked venturesomely on Document view, noticed that despite the ellipsis after the command name there was no farther interaction possible, observed change. Wanted to go back to Structure view: not there! The View menu has changed its position in the menu and offers different commands.

I'm sure people familiar with using the structured interface will take this in their stride, but as a new and mildly curious visitor I'd welcome some advice on this single point of switching a .ditamap between structure view and document view. Thanks in advance!