Locking an axis

[EDIT] If you are using the same search terms as me, find the answer here:
http://discourse.mcneel.com/t/how-to-draw-in-a-locked-plane/14559

[SOLVED] Hey guys,

I’m looking for a similar kind of lock, but rather for a plane, instead of 1 axis.

  • I’m tracing a drawing, and objects based on different heights on the Z axis,
  • I am using and do want to use snapping.
  • I want to the snapping to ignore the Z axis and keep in the same XY plane I started my first point at.

How can I do this? There should be an easier way to create planar polylines/curves instead of having to pull all the points to the same Z height, or to have to project every curve I make.