Hi Dan, MoI does not quite have the exact same type of direction lock as Rhino. But there are a couple of different things you can do.

If you want to force things along an axis line when you're using "straight snap" (called ortho in Rhino), you can force that to be on by holding down the shift key.

Then the other way is if you want to track points along some arbitrary line you can drag out a construction line along the line you want. It is also possible to then restrict the next point to be locked onto that line by holding down for a second on the little launcher tag that shows up after you make a construction line. If you pick "Project next pt" on that little construction line menu that will work similar to tab direction lock.

It's generally intended that the construction line mechanism in MoI replaces all those various different modes and special modifier key combos that are set up in Rhino. I may put in a tab direction lock thing back in though in the future.

- Michael