O-X-Y Type Attachment Modes

Here we provide more detailed information on the use of Align O-X-Y type modes in the Part_EditAttachment attachment editor. These modes are These modes are used to attach to a specified vertex, with an orientation determined by reference to other vertices or edges.
 * Align O-X-Y
 * Align O-X-Z
 * Align O-Y-X
 * Align O-Y-Z
 * Align O-Z-X
 * Align O-Z-Y

must be a Vertex. The origin is mapped to this selected point.

and must be either Vertices or Edges. They provide direction information. For a Vertex, the direction is from the origin to the selected vertex. For an Edge it is the direction of the edge. is optional.

Take mode O-X-Z as an example.
 * The 'O' represents the origin, corresponding to the.
 * The 'X' indicates that the X-axis of the attached object is to be aligned with the direction of
 * The 'Z' indicates that the Z-axis of the attached object is to be aligned with the component of the direction of at right angles to the X-axis.
 * The 'Y'-axis completes the orthogonal right-hand axis triad.

For other modes, the axes are mapped in the corresponding fashion.

If is not provided, FreeCAD makes default choices for it. For modes O-X-Y, O-X-Z, O-Y-X and O-Y-Z is taken to align with the global Z-axis. For modes O-Z-X and O-Z-Y is taken to be the global Y-axis.