Segment vs plane intersection.
set to the point of intersection
set to the point's progress between endpoints a at 0.0 and b at 1.0, or T.infinity if parallel to the plane
true if the segment crosses the plane exactly once, or false if the segment is parallel to or does not reach the plane
"Geometry for Computer Graphics: Formulae, Examples and Proofs", Vince (2005), p. 62
See Implementation
Segment vs plane intersection.