constrain movement

how do I constrain the movement of a component.
Lets say I have a vert I want to move and constrain its movement along an edge.
how can i do that.
I know max can do it and I have seen it done in Blender in a video, but i cant find it again

If the goal is to get a vertex to move along the edge it’s attached to you can set your pivot to “active element” then select the vertex you want to move, hold shift and select the vertex at the other end of the edge. Now when you scale it, it will move toward the last one you selected.

You can also do edge slide for connected edges, ctrl E. There are also edge rotating tools under the same menu.

Of course you can always place the cursor somewhere with ctrl S and set you pivot to the cursor then scale a vertex towards the cursor.

“vertex to move along the edge it’s attached to you can set your pivot to “active element” then select the vertex you want to move, hold shift and select the vertex at the other end of the edge. Now when you scale it, it will move toward the last one you selected.”

That is it.
thanks very much