When I select objects and use one of the align commands, what moves and what stays put?

In Prism 6, you can select two or more objects on a graph or layout, and then use one of the align commands to get them lined up. But lined up with what? Prism first constructs (in its "mind" anyway) a rectangle that encloses all the selected objects. Then it aligns with the edges of that rectangle. If you ask to align left, it moves all the objects to align with the left edge of that rectangle. If you ask to align right, all objects align with the right side of that rectangle. Etc. It pays no attention to whether any object is locked or not, and moves (aligns) locked objects as if they are not locked.