B-spline control point format

Does Graphviz use quadratic or cubic B-splines for edges, or both?  When reading control points from the plain output format, can one assume:
1.  The first and last points are touched by the B-spline
2.  There are always at least 3+2k (quadratic) or 4+3k (cubic) control points?
Thanks.

B-spline control point

> Does Graphviz use quadratic or cubic B-splines for edges, or both?
Cubic B-splines.
> 1.  The first and last points are touched by the B-spline
First and last points of what? If there are no arrowheads, the first and last points of the B-spline will, by default, lie on the boundary of the tail and head nodes, respectively. If there are arrowheads, things are more complex. See the note under http://www.graphviz.org/content/output-formats#dplain.
> 2.  There are always at least 3+2k (quadratic) or 4+3k (cubic) control points?
The latter.
 
Keep in mind that the plain format is very simple (intentionally), so it may not provide all the information one might want.

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