    path.closestPointTangent(point [, opt])

Return a line that is tangent to the path at the point that lies closest to `point`.

If the identified closest point is a point of discontinuity (e.g. it is a point shared by two Lineto segments with different slopes), the tangent line is constructed for the earlier segment (i.e. the segment closer to the beginning of the path).

The tangent line starts at the identified closest point. The direction from `start` to `end` is the same as the direction of the curve at the closest point.

The algorithm skips over segments that are not differentiable. This includes all invisible segments (e.g. Moveto segments) and visible segments with zero length. If the path contains no valid segments, `null` is returned. If the path has no segments at all, `null` is returned, as well. The `segment.isDifferentiable()` functions may be used to determine whether a given segment is valid; the `path.isDifferentiable()` function may be used to determine whether the path contains at least one valid segment.

The function finds a valid segment whose identified closest point lies at the lowest distance from `point`. It then finds a tangent to the segment at the identified closest point.

The `opt` argument is optional. Two properties may be specified, `opt.precision` and `opt.segmentSubdivisions`, which determine maximum error allowed in segment `closestPoint` calculations for curved segments (default precision is 3; this corresponds to maximum observed error of 0.1%). The `opt.segmentSubdivisions` property is an array of individual segments' subdivision arrays. The `path.getSegmentSubdivisions()` function may be used to obtain the `segmentSubdivisions` array. The `opt.precision` property is still necessary, however; it determines the precision of the point search algorithm in curved segments.