A lone object selected with ruler guides can be the key (the Selection
tool's click on it), and Align to the key moves the other selected
guides to its edge or centre: vertical guides to left, centre or right,
horizontal ones to top, centre or bottom. Parallel guides line up on a
key guide. Aligning to the selection or the artboard leaves guides alone.
A click with the Selection tool on a guide selected with objects makes
it the key (select.key {guide}), drawn thicker; a click on it again
cancels it. Align to Key Object is on with one object and a selected
guide and makes the guide the key. object.align lines the objects (or
selected anchors) up on the guide's line and leaves the guide where it
is: a vertical guide sets x only, a horizontal one y. The selection
keeps key_guide beside key, never both; it goes with the guide or the
objects, and follows the guide when earlier guides are deleted.
Distribute Spacing doesn't space from a key guide.
Dan Green