doc tweaks

attachments.scad

@@ -2348,13 +2348,13 @@ module edge_profile(edges=EDGES_ALL, except=[], excess=0.01, convexity=10) {
 //     2. Top
 //     3. Front or Back
 //   . 
-//   What this means is that if an edge string contains any edge on the bottom then the bottom edges will be oriented to joint the bottom face
+//   What this means is that if an edge string contains any edge on the bottom then the bottom edges will be oriented to join the bottom face
-//   to something, and the rest of the string consistently oriented.  If no bottom edges are present but top edges are present then the
+//   to something, and the rest of the string consistently oriented.  If the string contains no bottom edges but it has top edges then 
-//   string will be oriented so that it can join its top face to something.  If no top or bottom edges are present, then the edge (which must
+//   the edge string will be oriented so that the object can join its top face to something.  If the string has no top or bottom edges then it
-//   be just a single edge) will be oriented so that either the front or back face of the cube can make a smooth joint.
+//   must be just a single edge and it will be is oriented so that either the front or back face of the cube can make a smooth joint.
 //   If the edge orientation is reversed from what you need, set `flip=true`.  If these rules seem complicated, just create your model,
-//   examine the edges, and flip them as required.  Note that creating fillets with {{yflip()}} may partially work but is **not** the correct
+//   examine the edges, and flip them as required.  Note that creating fillets with {{yflip()}} may seem similar to setting `flip=true` and
-//   way to flip edges and can produce incomplete results.  
+//   may partially work but is **not** the correct way to flip edge profile; it can produce incomplete results.  
 //   
 // Arguments:
 //   edges = Edges to mask.  See [Specifying Edges](attachments.scad#subsection-specifying-edges).  Default: All edges.

vnf.scad

@@ -1418,6 +1418,18 @@ function _slice_3dpolygons(polys, dir, cuts) =
 //   vnf_polyhedron([VNF, VNF, VNF, ...]) [ATTACHMENTS];
 // Description:
 //   Given a VNF structure, or a list of VNF structures, creates a polyhedron from them.
+//   .
+//   An arbitrary VNF may not have a geometry that matches well with the anchoring system.  The anchors are
+//   automatically generated using one of two methods, the "hull" anchor type and the "intersect" anchor type.  
+//   The "hull" method is the default.  It finds an anchor point on the convex hull of the shape.  It does this
+//   by taking a plane normal to the anchor direction and and shifting it to the most distant point on the VNF.
+//   This plane may intersect the VNF in one point, several points, or even a face.  If it intersects in a face
+//   the anchor is the face centroid.  Otherwise the anchor is the mean of the vertices of VNF that intersect the
+//   plane.  The anchor direction will be the direction you originally specified.  
+//   .
+//   The "intersect" method creates a ray based at the VNF center point that points in the anchor direction and
+//   chooses the most distant intersection point as the anchor.  In this case, the anchor direction is
+//   computed from the VNF geometry based on the face or edge where that intersection point lies.  
 // Arguments:
 //   vnf = A VNF structure, or list of VNF structures.
 //   convexity = Max number of times a line could intersect a wall of the shape.