Fixed 2D Constraint: "Fixes the end points and direction of a linear segment or the center point of a circular element to its current position in the plane."
There needs to be some more thought about what is meant and needed when something is 'fixed'. Inevitably you are talking about fixing to 'something'. That something is not just the x,y.z coordinates or the x,y coordinates according to a plane.The user will inevitably need to fix one or two of the x,y,z coordinates only. See Solidwork's Along X/Y etc.
Z coordinate fixing is implied by the 2d Constraint tool selection, but it would also be good to define this as this will allow points to be offset from the 2d solving / sketch plane.
Fixed 3D Constraint: "Used to fix the linear and rotary movement of a 3D element."
Fix Vertex: it would be good to allow the x,y,z coordinates to be fixed individually as per above.
Fiex Edge: it would be good to able to fix the rotation angle independently of the translation axis. The user should be able to define the angle (numerically/accudraw/expressions). The translation direction and distance should also be definable 'Global x,y,z axis' or by ACS. Max/min using expressions.
Fix Surface: it would be good to allow the x,y,z coordinates to be fixed individually as per above. Same for Rotation z axis. The Rotation axis should be defineable.
Fix Element: it would be good to allow the x,y,z coordinates to be fixed individually as per above. Same for Rotation x,y,z axes. The Element's Rotation axis pivot point should be defineable.