Hi John, hi folks.
The Dimension Tool will auto select a full line or a full arc or a full polygon or a full circle if the cursor is placed on the line or any edge of the other entities.
The Dimension Tool, however, can attach dimension lines to points (endpoint, midpoints, center points and construction points).
So, for some nice effects, you can add temporary points or edges from which you will use one or two endpoints to attach the ends of a dimension line. When done, simply delete the temporary geometry.
Even better, dimension items can be moved and rotated and can also be used with the Move/Copy and Rotate/Copy feature to get linear and radial arrays.
Just ideas.