Summary
I isolated the dragging portion of update 3 of the reusable calendar project to show what options under the draggable jQuery UI to use.
In the draggable() function, I used the grid: [0, 15] to restrict its movement to 15 px vertical, then I used containment: [0, y1, 0, y2], where y1 is the offsetTop value of the strip itself when it’s at the last month/digit, and y2 is at the first month/digit, to restrict its range so the strip won’t go past the first and last value.