diff --git a/.openscad_docsgen_rc b/.openscad_docsgen_rc
index e49a310..1e93946 100644
--- a/.openscad_docsgen_rc
+++ b/.openscad_docsgen_rc
@@ -69,7 +69,7 @@ PrioritizeFiles:
   walls.scad
   wiring.scad
 DefineHeader(BulletList): Side Effects
-DefineHeader(Table;Headers=Anchor Name|Position): Extra Anchors
+DefineHeader(Table;Headers=Anchor Name|Position): Named Anchors
 DefineHeader(Table;Headers=Anchor Type|What it is): Anchor Types
 DefineHeader(Table;Headers=Name|Definition): Terminology
 DefineHeader(BulletList): Requirements
diff --git a/attachments.scad b/attachments.scad
index 1cc3685..fe3cd9b 100644
--- a/attachments.scad
+++ b/attachments.scad
@@ -2957,7 +2957,7 @@ function reorient(
     axis=UP, override, 
     geom,
     p=undef
-) =
+) = 
     assert(is_undef(anchor) || is_vector(anchor) || is_string(anchor), str("Got: ",anchor))
     assert(is_undef(spin)   || is_vector(spin,3) || is_num(spin), str("Got: ",spin))
     assert(is_undef(orient) || is_vector(orient,3), str("Got: ",orient))
@@ -3571,7 +3571,7 @@ function _force_anchor_2d(anchor) =
 ///   geom = The geometry description of the shape.
 function _find_anchor(anchor, geom) =
     is_string(anchor)? (
-          anchor=="origin"? [anchor, CENTER, UP, 0]
+          anchor=="origin"? [anchor, CENTER, UP, 0]    // Ok that this returns 3d anchor in the 2d case?
         : let(
               anchors = last(geom),
               found = search([anchor], anchors, num_returns_per_match=1)[0]
diff --git a/bottlecaps.scad b/bottlecaps.scad
index 0a15080..8e398f9 100644
--- a/bottlecaps.scad
+++ b/bottlecaps.scad
@@ -31,7 +31,7 @@ include <rounding.scad>
 //   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `CENTER`
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
 //   orient = Vector to rotate top towards, after spin.  See [orient](attachments.scad#subsection-orient).  Default: `UP`
-// Extra Anchors:
+// Named Anchors:
 //   "tamper-ring" = Centered at the top of the anti-tamper ring channel.
 //   "support-ring" = Centered at the bottom of the support ring.
 // Example:
@@ -160,7 +160,7 @@ function  pco1810_neck(wall=2, anchor="support-ring", spin=0, orient=UP) =
 //   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `CENTER`
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
 //   orient = Vector to rotate top towards, after spin.  See [orient](attachments.scad#subsection-orient).  Default: `UP`
-// Extra Anchors:
+// Named Anchors:
 //   "inside-top" = Centered on the inside top of the cap.
 // Examples:
 //   pco1810_cap();
@@ -236,7 +236,7 @@ function pco1810_cap(h, r, d, wall, texture="none", anchor=BOTTOM, spin=0, orien
 //   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `CENTER`
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
 //   orient = Vector to rotate top towards, after spin.  See [orient](attachments.scad#subsection-orient).  Default: `UP`
-// Extra Anchors:
+// Named Anchors:
 //   "tamper-ring" = Centered at the top of the anti-tamper ring channel.
 //   "support-ring" = Centered at the bottom of the support ring.
 // Example:
@@ -362,7 +362,7 @@ function pco1881_neck(wall=2, anchor="support-ring", spin=0, orient=UP) =
 //   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `CENTER`
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
 //   orient = Vector to rotate top towards, after spin.  See [orient](attachments.scad#subsection-orient).  Default: `UP`
-// Extra Anchors:
+// Named Anchors:
 //   "inside-top" = Centered on the inside top of the cap.
 // Examples:
 //   pco1881_cap();
@@ -431,7 +431,7 @@ function pco1881_cap(wall=2, texture="none", anchor=BOTTOM, spin=0, orient=UP) =
 //   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `CENTER`
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
 //   orient = Vector to rotate top towards, after spin.  See [orient](attachments.scad#subsection-orient).  Default: `UP`
-// Extra Anchors:
+// Named Anchors:
 //   "support-ring" = Centered at the bottom of the support ring.
 // Example:
 //   generic_bottle_neck();
@@ -564,7 +564,7 @@ function generic_bottle_neck(
 //   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `CENTER`
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
 //   orient = Vector to rotate top towards, after spin.  See [orient](attachments.scad#subsection-orient).  Default: `UP`
-// Extra Anchors:
+// Named Anchors:
 //   "inside-top" = Centered on the inside top of the cap.
 // Examples:
 //   generic_bottle_cap(thread_depth=2,neck_od=INCH,height=INCH/2);
diff --git a/gears.scad b/gears.scad
index 658a039..387d8cc 100644
--- a/gears.scad
+++ b/gears.scad
@@ -1643,7 +1643,7 @@ module ring_gear2d(
 //   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `CENTER`
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
 //   orient = Vector to rotate top towards, after spin.  See [orient](attachments.scad#subsection-orient).  Default: `UP`
-// Extra Anchors:
+// Named Anchors:
 //   "root" = At the base of the teeth, at the center of rack.
 //   "root-left" = At the base of the teeth, at the left end of the rack.
 //   "root-right" = At the base of the teeth, at the right end of the rack.
@@ -1912,7 +1912,7 @@ function rack(
 //   rounding = If true, rack tips and valleys are slightly rounded.  Default: true
 //   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `CENTER`
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
-// Extra Anchors:
+// Named Anchors:
 //   "root" = At the height of the teeth, at the center of rack.
 //   "root-left" = At the height of the teeth, at the left end of the rack.
 //   "root-right" = At the height of the teeth, at the right end of the rack.
@@ -2363,7 +2363,7 @@ module crown_gear(
 //   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: "pitchbase"
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
 //   orient = Vector to rotate top towards, after spin.  See [orient](attachments.scad#subsection-orient).  Default: `UP`
-// Extra Anchors:
+// Named Anchors:
 //   "pitchbase" = With the base of the pitch cone in the XY plane, centered at the origin.  This is the natural height for the gear, and the default anchor.
 //   "apex" = At the pitch cone apex for the bevel gear.
 //   "flattop" = At the top of the flat top of the bevel gear.
diff --git a/masks3d.scad b/masks3d.scad
index 0774217..aebbf60 100644
--- a/masks3d.scad
+++ b/masks3d.scad
@@ -249,20 +249,6 @@ module chamfer_cylinder_mask(r, chamfer, d, ang=45, from_end=false, anchor=CENTE
 //               rounding_edge_mask(l=p.z, r=25);
 //       }
 //   }
-// Example: Acute angle 
-//   ang=60;
-//   difference() {
-//       pie_slice(ang=ang, h=50, r=100);
-//       zflip_copy(z=25)
-//          #rounding_corner_mask(r=20, ang=ang);
-//   }
-// Example: Obtuse angle 
-//   ang=120;
-//   difference() {
-//       pie_slice(ang=ang, h=50, r=30);
-//       zflip_copy(z=25)
-//          #rounding_corner_mask(r=20, ang=ang);
-//   }
 
 function rounding_edge_mask(l, r, ang=90, r1, r2, d, d1, d2, excess=0.1, anchor=CENTER, spin=0, orient=UP, h,height,length) = no_function("rounding_edge_mask");
 module rounding_edge_mask(l, r, ang=90, r1, r2, excess=0.01, d1, d2,d,r,length, h, height, anchor=CENTER, spin=0, orient=UP,
@@ -274,7 +260,7 @@ module rounding_edge_mask(l, r, ang=90, r1, r2, excess=0.01, d1, d2,d,r,length,
     dummy = assert(all_nonnegative([r1,r2]), "radius/diameter value(s) must be nonnegative")
             assert(all_positive([length]), "length/l/h/height must be a positive value")
             assert(is_finite(ang) && ang>0 && ang<180, "ang must be a number between 0 and 180");
-    steps = ceil(segs(r)*(180-ang)/360);
+    steps = ceil(segs(max(r1,r2))*(180-ang)/360);
     function make_path(r) =
         let(
              arc = r==0 ? repeat([0,0],steps+1)
@@ -383,8 +369,21 @@ module rounding_edge_mask(l, r, ang=90, r1, r2, excess=0.01, d1, d2,d,r,length,
 //       corner_mask(TOP)
 //           #rounding_corner_mask(r=20);
 //   }
-// Example: Acute angle mask
-// 
+// Example(VPR=[71.8,0,345.8],VPT=[57.0174,43.8496,24.5863],VPD=263.435,NoScales): Acute angle 
+//   ang=60;
+//   difference() {
+//       pie_slice(ang=ang, h=50, r=100);
+//       zflip_copy(z=25)
+//          #rounding_corner_mask(r=20, ang=ang);
+//   }
+// Example(VPR=[62.7,0,5.4],VPT=[6.9671,22.7592,20.7513],VPD=192.044): Obtuse angle 
+//   ang=120;
+//   difference() {
+//       pie_slice(ang=ang, h=50, r=30);
+//       zflip_copy(z=25)
+//          #rounding_corner_mask(r=20, ang=ang);
+//   }
+
 function rounding_corner_mask(r, ang, d, style="octa", excess=0.1, anchor=CENTER, spin=0, orient=UP) = no_function("rounding_corner_mask");
 module rounding_corner_mask(r, ang=90, d, style="octa", excess=0.1, anchor=CENTER, spin=0, orient=UP)
 {
diff --git a/math.scad b/math.scad
index d59d159..bb5be7a 100644
--- a/math.scad
+++ b/math.scad
@@ -1374,7 +1374,7 @@ function quadratic_roots(a,b,c,real=false) =
 
 
 // Function: polynomial() 
-// Synopsis: Calculates a polynomial equation at a given value.
+// Synopsis: Evaluate a polynomial at a real or complex value.
 // Topics: Math, Complex Numbers
 // See Also: quadratic_roots(), polynomial(), poly_mult(), poly_div(), poly_add(), poly_roots()
 // Usage:
@@ -1394,7 +1394,7 @@ function polynomial(p,z,k,total) =
 
 
 // Function: poly_mult()
-// Synopsis: Returns the polynomial result of multiplying two polynomial equations.
+// Synopsis: Compute product of two polynomials, returning a polynomial.
 // Topics: Math
 // See Also: quadratic_roots(), polynomial(), poly_mult(), poly_div(), poly_add(), poly_roots()
 // Usage:
@@ -1416,7 +1416,7 @@ function poly_mult(p,q) =
 
     
 // Function: poly_div()
-// Synopsis: Returns the polynomial quotient and remainder results of dividing two polynomial equations.
+// Synopsis: Returns the polynomial quotient and remainder results of dividing two polynomials.
 // Topics: Math
 // See Also: quadratic_roots(), polynomial(), poly_mult(), poly_div(), poly_add(), poly_roots()
 // Usage:
@@ -1457,7 +1457,7 @@ function _poly_trim(p,eps=0) =
 
 
 // Function: poly_add()
-// Synopsis: Returns the polynomial sum of adding two polynomial equations.
+// Synopsis: Returns the polynomial sum of adding two polynomials.
 // Topics: Math
 // See Also: quadratic_roots(), polynomial(), poly_mult(), poly_div(), poly_add(), poly_roots()
 // Usage:
@@ -1475,7 +1475,7 @@ function poly_add(p,q) =
 
 
 // Function: poly_roots()
-// Synopsis: Returns all complex number roots of the given real polynomial.
+// Synopsis: Returns all complex valued roots of the given real polynomial.
 // Topics: Math, Complex Numbers
 // See Also: quadratic_roots(), polynomial(), poly_mult(), poly_div(), poly_add(), poly_roots()
 // Usage:
@@ -1563,7 +1563,8 @@ function _poly_roots(p, pderiv, s, z, tol, i=0) =
 //   parts are zero.  You can specify eps, in which case the test is
 //   z.y/(1+norm(z)) < eps.  Because
 //   of poor convergence and higher error for repeated roots, such roots may
-//   be missed by the algorithm because their imaginary part is large.
+//   be missed by the algorithm because error can make their imaginary parts
+//   large enough to appear non-zero.  
 // Arguments:
 //   p = polynomial to solve as coefficient list, highest power term first
 //   eps = used to determine whether imaginary parts of roots are zero
diff --git a/metric_screws.scad b/metric_screws.scad
index 556e5f0..695ba90 100644
--- a/metric_screws.scad
+++ b/metric_screws.scad
@@ -373,7 +373,7 @@ function get_metric_nut_thickness(size) = lookup(size, [
 //   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `CENTER`
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
 //   orient = Vector to rotate top towards, after spin.  See [orient](attachments.scad#subsection-orient).  Default: `UP`
-// Extra Anchors:
+// Named Anchors:
 //   "base" = At the base of the head.
 //   "countersunk" = At the head height that would be just barely exposed when countersunk.
 // Examples:
@@ -434,7 +434,7 @@ module generic_screw(
 //   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `CENTER`
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
 //   orient = Vector to rotate top towards, after spin.  See [orient](attachments.scad#subsection-orient).  Default: `UP`
-// Extra Anchors:
+// Named Anchors:
 //   "base" = At the base of the head.
 //   "countersunk" = At the head height that would be just barely exposed when countersunk.
 //   "shank" = At the bottom start of the unthreaded shank.
diff --git a/regions.scad b/regions.scad
index e602c91..9175da7 100644
--- a/regions.scad
+++ b/regions.scad
@@ -314,6 +314,8 @@ function force_region(poly) = is_path(poly) ? [poly] : poly;
 //   spin = Rotate this many degrees after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
 //   cp = Centerpoint for determining intersection anchors or centering the shape.  Determintes the base of the anchor vector.  Can be "centroid", "mean", "box" or a 2D point.  Default: "centroid"
 //   atype = Set to "hull" or "intersect" to select anchor type.  Default: "hull"
+// Named Anchors:
+//   "origin" = The native position of the region.
 // Anchor Types:
 //   "hull" = Anchors to the virtual convex hull of the region.
 //   "intersect" = Anchors to the outer edge of the region.
@@ -1192,6 +1194,8 @@ function _list_three(a,b,c) =
 //   When called as a function and given a list of regions or 2D polygons,
 //   returns the union of all given regions and polygons.  Result is a single region.
 //   When called as the built-in module, makes the union of the given children.
+//   This function is **much** slower than the native union module acting on geometry,
+//   so you should only use it when you need a point list for further processing.  
 // Arguments:
 //   regions = List of regions to union.
 // Example(2D):
@@ -1227,6 +1231,8 @@ function union(regions=[],b=undef,c=undef,eps=EPSILON) =
 //   takes the first region or polygon and differences away all other regions/polygons from it.  The resulting
 //   region is returned.
 //   When called as the built-in module, makes the set difference of the given children.
+//   This function is **much** slower than the native difference module acting on geometry,
+//   so you should only use it when you need a point list for further processing.  
 // Arguments:
 //   regions = List of regions or polygons to difference.
 // Example(2D):
@@ -1299,6 +1305,8 @@ function intersection(regions=[],b=undef,c=undef,eps=EPSILON) =
 //   When called as a module, performs a Boolean exclusive-or of up to 10 children.  Note that when
 //   the input regions cross each other the exclusive-or operator will produce shapes that
 //   meet at corners (non-simple regions), which do not render in CGAL.  
+//   This function is **much** slower than the native intersection module acting on geometry,
+//   so you should only use it when you need a point list for further processing.  
 // Arguments:
 //   regions = List of regions or polygons to exclusive_or
 // Example(2D): As Function.  A linear_sweep of this shape fails to render in CGAL.  
diff --git a/rounding.scad b/rounding.scad
index 10c1c76..cf8e59a 100644
--- a/rounding.scad
+++ b/rounding.scad
@@ -951,6 +951,11 @@ function _path_join(paths,joint,k=0.5,i=0,result=[],relocate=true,closed=false)
 //   spin = Rotate this many degrees after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
 //   cp = Centerpoint for determining intersection anchors or centering the shape.  Determintes the base of the anchor vector.  Can be "centroid", "mean", "box" or a 2D point.  Default: "centroid"
 //   atype = Set to "hull" or "intersect" to select anchor type.  Default: "hull"
+// Named Anchors:
+//   "origin" = The native position of the region.
+// Anchor Types:
+//   "hull" = Anchors to the virtual convex hull of the region.
+//   "intersect" = Anchors to the outer edge of the region.
 // Example(2D):  Basic examples illustrating flat, round, and pointed ends, on a finely sampled arc and a path made from 3 segments.
 //   arc = arc(points=[[1,1],[3,4],[6,3]],n=50);
 //   path = [[0,0],[6,2],[9,7],[8,10]];
@@ -1047,7 +1052,7 @@ function _path_join(paths,joint,k=0.5,i=0,result=[],relocate=true,closed=false)
 //   right(12)
 //     offset_stroke(path, width=1, closed=true);
 function offset_stroke(path, width=1, rounded=true, start, end, check_valid=true, quality=1, chamfer=false, closed=false,
-                       atype="hull", anchor, spin, cp="centroid") =
+                       atype="hull", anchor="origin", spin, cp="centroid") =
         let(path = force_path(path))
         assert(is_path(path,2),"path is not a 2d path")
         let(
@@ -1091,7 +1096,7 @@ function offset_stroke(path, width=1, rounded=true, start, end, check_valid=true
                           reverse(slice(right_path,startpath[2],-1-endpath[1])),
                           startpath[0]
                   )
-         )
+         ) 
          reorient(anchor=anchor, spin=spin, two_d=true, path=pts, extent=atype=="hull", cp=cp, p=pts);
 
 function os_pointed(dist,loc=0) =
@@ -1374,7 +1379,7 @@ module offset_stroke(path, width=1, rounded=true, start, end, check_valid=true,
 //   intersect = Anchors to the surface of the linear sweep of the path, ignoring any end roundings.
 //   surf_hull = Anchors to the convex hull of the offset_sweep shape, including end treatments.
 //   surf_intersect = Anchors to the surface of the offset_sweep shape, including any end treatments.
-// Extra Anchors:
+// Named Anchors:
 //   "base" = Anchor to the base of the shape in its native position, ignoring any "extra"
 //   "top" = Anchor to the top of the shape in its native position, ignoring any "extra"
 //   "zcenter" = Center shape in the Z direction in the native XY position, ignoring any "extra"
@@ -2082,6 +2087,11 @@ function _rp_compute_patches(top, bot, rtop, rsides, ktop, ksides, concave) =
 //   orient = Vector to rotate top towards after spin  (module only)
 //   atype = Select "hull" or "intersect" anchor types.  (module only) Default: "hull"
 //   cp = Centerpoint for determining "intersect" anchors or centering the shape.  Determintes the base of the anchor vector.  Can be "centroid", "mean", "box" or a 3D point.  (module only) Default: "centroid"
+// Named Anchors:
+//   "origin" = The native position of the prism.
+// Anchor Types:
+//   "hull" = Anchors to the virtual convex hull of the prism. 
+//   "intersect" = Anchors to the surface of the prism.
 // Example: Uniformly rounded pentagonal prism
 //   rounded_prism(pentagon(3), height=3,
 //                 joint_top=0.5, joint_bot=0.5, joint_sides=0.5);
@@ -2792,7 +2802,7 @@ Access to the derivative smoothing parameter?
 //   orient = Vector to rotate top towards after spin  (module only)
 //   atype = Select "hull" or "intersect" anchor types.  (module only) Default: "hull"
 //   cp = Centerpoint for determining "intersect" anchors or centering the shape.  Determintes the base of the anchor vector.  Can be "centroid", "mean", "box" or a 3D point.  (module only) Default: "centroid"
-// Extra Anchors:
+// Named Anchors:
 //   "root" = Root point of the joiner prism, pointing out in the direction of the prism axis
 //   "end" = End point of the joiner prism, pointing out in the direction of the prism axis
 // Example(3D,NoScales): Here is the simplest case, a circular prism with a specified length standing vertically on a plane.  
diff --git a/screws.scad b/screws.scad
index 172ff07..632459c 100644
--- a/screws.scad
+++ b/screws.scad
@@ -277,22 +277,22 @@ Torx values:  https://www.stanleyengineeredfastening.com/-/media/web/sef/resourc
 //   shaft = screw shaft
 //   shank = unthreaded section of shaft (invalid if screw is fully threaded)
 //   threads = threaded section of screw     
-// Extra Anchors:
-//   top = top of screw
-//   bot = bottom of screw
-//   center = center of screw
-//   head_top = top of head (same as top for headless screws)
-//   head_bot = bottom of head (same as top for headless screws)
-//   head_center = center of head (same as top for headless screws)
-//   shaft_top = top of shaft
-//   shaft_bot = bottom of shaft
-//   shaft_center = center of shaft
-//   shank_top = top of shank (invalid if screw is fully threaded)
-//   shank_bot = bottom of shank (invalid if screw is fully threaded)
-//   shank_center = center of shank (invalid if screw is fully threaded)
-//   threads_top = top of threaded portion of screw (invalid if thread_len=0)
-//   threads_bot = bottom of threaded portion of screw (invalid if thread_len=0)
-//   threads_center = center of threaded portion of screw (invalid if thread_len=0)
+// Named Anchors:
+//   "top" = top of screw
+//   "bot" = bottom of screw
+//   "center" = center of screw
+//   "head_top" = top of head (same as top for headless screws)
+//   "head_bot" = bottom of head (same as top for headless screws)
+//   "head_center" = center of head (same as top for headless screws)
+//   "shaft_top" = top of shaft
+//   "shaft_bot" = bottom of shaft
+//   "shaft_center" = center of shaft
+//   "shank_top" = top of shank (invalid if screw is fully threaded)
+//   "shank_bot" = bottom of shank (invalid if screw is fully threaded)
+//   "shank_center" = center of shank (invalid if screw is fully threaded)
+//   "threads_top" = top of threaded portion of screw (invalid if thread_len=0)
+//   "threads_bot" = bottom of threaded portion of screw (invalid if thread_len=0)
+//   "threads_center" = center of threaded portion of screw (invalid if thread_len=0)
 // Example(Med): Selected UTS (English) screws
 //   $fn=32;
 //   xdistribute(spacing=8){
@@ -803,22 +803,22 @@ module screw(spec, head, drive, thread, drive_size,
 //   shaft = screw shaft
 //   shank = unthreaded section of shaft (invalid if screw is fully threaded)
 //   threads = threaded section of screw     
-// Extra Anchors:
-//   top = top of screw
-//   bot = bottom of screw
-//   center = center of screw
-//   head_top = top of head (invalid for headless screws)
-//   head_bot = bottom of head (invalid for headless screws)
-//   head_center = center of head (invalid for headless screws)
-//   shaft_top = top of shaft
-//   shaft_bot = bottom of shaft
-//   shaft_center = center of shaft
-//   shank_top = top of shank (invalid if screw is fully threaded)
-//   shank_bot = bottom of shank (invalid if screw is fully threaded)
-//   shank_center = center of shank (invalid if screw is fully threaded)
-//   threads_top = top of threaded portion of screw (invalid if thread_len=0)
-//   threads_bot = bottom of threaded portion of screw (invalid if thread_len=0)
-//   threads_center = center of threaded portion of screw (invalid if thread_len=0)
+// Named Anchors:
+//   "top" = top of screw
+//   "bot" = bottom of screw
+//   "center" = center of screw
+//   "head_top" = top of head (invalid for headless screws)
+//   "head_bot" = bottom of head (invalid for headless screws)
+//   "head_center" = center of head (invalid for headless screws)
+//   "shaft_top" = top of shaft
+//   "shaft_bot" = bottom of shaft
+//   "shaft_center" = center of shaft
+//   "shank_top" = top of shank (invalid if screw is fully threaded)
+//   "shank_bot" = bottom of shank (invalid if screw is fully threaded)
+//   "shank_center" = center of shank (invalid if screw is fully threaded)
+//   "threads_top" = top of threaded portion of screw (invalid if thread_len=0)
+//   "threads_bot" = bottom of threaded portion of screw (invalid if thread_len=0)
+//   "threads_center" = center of threaded portion of screw (invalid if thread_len=0)
 // Example: Counterbored clearance hole
 //   diff()
 //     cuboid(20)
@@ -1037,22 +1037,22 @@ module screw_hole(spec, head, thread, oversize, hole_oversize, head_oversize,
 //   shoulder = the shoulder
 //   shaft = screw shaft
 //   threads = threaded section of screw     
-// Extra Anchors:
-//   top = top of screw
-//   bot = bottom of screw
-//   center = center of screw
-//   head_top = top of head (invalid for headless screws)
-//   head_bot = bottom of head (invalid for headless screws)
-//   head_center = center of head (invalid for headless screws)
-//   shoulder_top = top of shoulder
-//   shoulder_bot = bottom of shoulder
-//   shoulder_center = center of shoulder
-//   shaft_top = top of shaft
-//   shaft_bot = bottom of shaft
-//   shaft_center = center of shaft
-//   threads_top = top of threaded portion of screw (invalid if thread_len=0)
-//   threads_bot = bottom of threaded portion of screw (invalid if thread_len=0)
-//   threads_center = center of threaded portion of screw (invalid if thread_len=0)
+// Named Anchors:
+//   "top" = top of screw
+//   "bot" = bottom of screw
+//   "center" = center of screw
+//   "head_top" = top of head (invalid for headless screws)
+//   "head_bot" = bottom of head (invalid for headless screws)
+//   "head_center" = center of head (invalid for headless screws)
+//   "shoulder_top" = top of shoulder
+//   "shoulder_bot" = bottom of shoulder
+//   "shoulder_center" = center of shoulder
+//   "shaft_top" = top of shaft
+//   "shaft_bot" = bottom of shaft
+//   "shaft_center" = center of shaft
+//   "threads_top" = top of threaded portion of screw (invalid if thread_len=0)
+//   "threads_bot" = bottom of threaded portion of screw (invalid if thread_len=0)
+//   "threads_center" = center of threaded portion of screw (invalid if thread_len=0)
 // Example: ISO shoulder screw
 //   shoulder_screw("iso",10,length=20);
 // Example: English shoulder screw
diff --git a/shapes2d.scad b/shapes2d.scad
index 87da086..9e2a2ee 100644
--- a/shapes2d.scad
+++ b/shapes2d.scad
@@ -549,7 +549,7 @@ function ellipse(r, d, realign=false, circum=false, uniform=false, anchor=CENTER
 //   align_side = If given as a 2D vector, rotates the whole shape so that the normal of side0 points in that direction.  This occurs before spin.
 //   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `CENTER`
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
-// Extra Anchors:
+// Named Anchors:
 //   "tip0", "tip1", etc. = Each tip has an anchor, pointing outwards.
 //   "side0", "side1", etc. = The center of each side has an anchor, pointing outwards.
 // Example(2D): by Outer Size
@@ -691,7 +691,7 @@ module regular_ngon(n=6, r, d, or, od, ir, id, side, rounding=0, realign=false,
 //   align_side = If given as a 2D vector, rotates the whole shape so that the normal of side0 points in that direction.  This occurs before spin.
 //   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `CENTER`
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
-// Extra Anchors:
+// Named Anchors:
 //   "tip0" ... "tip4" = Each tip has an anchor, pointing outwards.
 //   "side0" ... "side4" = The center of each side has an anchor, pointing outwards.
 // Example(2D): by Outer Size
@@ -752,7 +752,7 @@ module pentagon(r, d, or, od, ir, id, side, rounding=0, realign=false, align_tip
 //   align_side = If given as a 2D vector, rotates the whole shape so that the normal of side0 points in that direction.  This occurs before spin.
 //   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `CENTER`
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
-// Extra Anchors:
+// Named Anchors:
 //   "tip0" ... "tip5" = Each tip has an anchor, pointing outwards.
 //   "side0" ... "side5" = The center of each side has an anchor, pointing outwards.
 // Example(2D): by Outer Size
@@ -812,7 +812,7 @@ module hexagon(r, d, or, od, ir, id, side, rounding=0, realign=false, align_tip,
 //   align_side = If given as a 2D vector, rotates the whole shape so that the normal of side0 points in that direction.  This occurs before spin.
 //   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `CENTER`
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
-// Extra Anchors:
+// Named Anchors:
 //   "tip0" ... "tip7" = Each tip has an anchor, pointing outwards.
 //   "side0" ... "side7" = The center of each side has an anchor, pointing outwards.
 // Example(2D): by Outer Size
@@ -863,8 +863,8 @@ module octagon(r, d, or, od, ir, id, side, rounding=0, realign=false, align_tip,
 //   ---
 //   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `CENTER`
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
-// Extra Anchors:
-//   hypot = Center of angled side, perpendicular to that side.
+// Named Anchors:
+//   "hypot" = Center of angled side, perpendicular to that side.
 // Example(2D):
 //   right_triangle([40,30]);
 // Example(2D): With `center=true`
@@ -1144,7 +1144,7 @@ module trapezoid(h, w1, w2, ang, shift, chamfer=0, rounding=0, flip=false, ancho
 //   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `CENTER`
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
 //   atype = Choose "hull" or "intersect" anchor methods.  Default: "hull"
-// Extra Anchors:
+// Named Anchors:
 //   "tip0" ... "tip4" = Each tip has an anchor, pointing outwards.
 //   "pit0" ... "pit4" = The inside corner between each tip has an anchor, pointing outwards.
 //   "midpt0" ... "midpt4" = The center-point between each pair of tips has an anchor, pointing outwards.
@@ -1439,7 +1439,7 @@ function teardrop2d(r, ang=45, cap_h, d, circum=false, realign=false, anchor=CEN
 //   d1 = diameter of the left-hand circle
 //   d2 = diameter of the right-hand circle
 //   D = diameter of the joining arcs
-// Extra Anchors:
+// Named Anchors:
 //   "left" = center of the left circle
 //   "right" = center of the right circle
 // Example(2D,NoAxes): This first example shows how the egg is constructed from two circles and two joining arcs.
@@ -1930,7 +1930,7 @@ function _superformula(theta,m1,m2,n1,n2=1,n3=1,a=1,b=1) =
 //   d = Diameter of the shape.  Scale shape to fit in a circle of diameter d.
 //   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `CENTER`
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
-// Extra Anchors:
+// Named Anchors:
 //   "tip0", "tip1", etc. = Each tip has an anchor, pointing outwards.
 // Examples(2D):
 //   reuleaux_polygon(n=3, r=50);
@@ -2025,7 +2025,7 @@ function reuleaux_polygon(n=3, r, d, anchor=CENTER, spin=0) =
 //   script = The script the text is in.  Default: `"latin"`
 //   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `"baseline"`
 //   spin = Rotate this many degrees around the Z axis.  See [spin](attachments.scad#subsection-spin).  Default: `0`
-// Extra Anchors:
+// Named Anchors:
 //   "baseline" = Anchors at the baseline of the text, at the start of the string.
 //   str("baseline",VECTOR) = Anchors at the baseline of the text, modified by the X and Z components of the appended vector.
 // Examples(2D):
diff --git a/shapes3d.scad b/shapes3d.scad
index dd9e596..d45589a 100644
--- a/shapes3d.scad
+++ b/shapes3d.scad
@@ -1120,10 +1120,10 @@ function rect_tube(
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
 //   orient = Vector to rotate top towards, after spin.  See [orient](attachments.scad#subsection-orient).  Default: `UP`
 //
-// Extra Anchors:
-//   hypot = Center of angled wedge face, perpendicular to that face.
-//   hypot_left = Left side of angled wedge face, bisecting the angle between the left side and angled faces.
-//   hypot_right = Right side of angled wedge face, bisecting the angle between the right side and angled faces.
+// Named Anchors:
+//   "hypot" = Center of angled wedge face, perpendicular to that face.
+//   "hypot_left" = Left side of angled wedge face, bisecting the angle between the left side and angled faces.
+//   "hypot_right" = Right side of angled wedge face, bisecting the angle between the right side and angled faces.
 //
 // Example: Centered
 //   wedge([20, 40, 15], center=true);
@@ -2741,10 +2741,10 @@ function torus(
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
 //   orient = Vector to rotate top towards, after spin.  See [orient](attachments.scad#subsection-orient).  Default: `UP`
 //
-// Extra Anchors:
-//   cap = The center of the top of the cap, oriented with the cap face normal.
-//   cap_fwd = The front edge of the cap.
-//   cap_back = The back edge of the cap.
+// Named Anchors:
+//   "cap" = The center of the top of the cap, oriented with the cap face normal.
+//   "cap_fwd" = The front edge of the cap.
+//   "cap_back" = The back edge of the cap.
 //
 // Example: Typical Shape
 //   teardrop(r=30, h=10, ang=30);
@@ -2862,9 +2862,9 @@ function teardrop(h, r, ang=45, cap_h, r1, r2, d, d1, d2, cap_h1, cap_h2,  chamf
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
 //   orient = Vector to rotate top towards, after spin.  See [orient](attachments.scad#subsection-orient).  Default: `UP`
 //
-// Extra Anchors:
-//   cap = The center of the top of the cap, oriented with the cap face normal.
-//   tip = The position where an un-capped onion would come to a point, oriented in the direction the point is from the center.
+// Named Anchors:
+//   "cap" = The center of the top of the cap, oriented with the cap face normal.
+//   "tip" = The position where an un-capped onion would come to a point, oriented in the direction the point is from the center.
 //
 // Example: Typical Shape
 //   onion(r=30, ang=30);
@@ -3365,10 +3365,12 @@ module fillet(l, r, ang=90, r1, r2, excess=0.01, d1, d2,d,length, h, height, anc
 //   surface where the height at any given point is the scalar value for that position.
 //   One script to convert a grayscale image to a heightfield array in a .scad file can be found at:
 //   https://raw.githubusercontent.com/BelfrySCAD/BOSL2/master/scripts/img2scad.py
+//   The bottom value defines a planar base for the resulting shape and it must be strictly less than
+//   the model data to produce valid geometry, so data which is too small is set to 0.1 units above the bottom value. 
 // Arguments:
 //   data = This is either the 2D rectangular array of heights, or a function literal that takes X and Y arguments.
 //   size = The [X,Y] size of the surface to create.  If given as a scalar, use it for both X and Y sizes. Default: `[100,100]`
-//   bottom = The Z coordinate for the bottom of the heightfield object to create.  Any heights lower than this will be truncated to very slightly above this height.  Default: -20
+//   bottom = The Z coordinate for the bottom of the heightfield object to create.  Any heights lower than this will be truncated to very slightly (0.1) above this height.  Default: -20
 //   maxz = The maximum height to model.  Truncates anything taller to this height.  Set to INF for no truncation.  Default: 100
 //   xrange = A range of values to iterate X over when calculating a surface from a function literal.  Default: [-1 : 0.01 : 1]
 //   yrange = A range of values to iterate Y over when calculating a surface from a function literal.  Default: [-1 : 0.01 : 1]
@@ -3437,7 +3439,7 @@ function heightfield(data, size=[100,100], bottom=-20, maxz=100, xrange=[-1:0.04
                     for (x = [0:1:xcnt-1]) [
                         size.x * (x/(xcnt-1)-0.5),
                         size.y * (y/(ycnt-1)-0.5),
-                        min(data[y][x],maxz)
+                        min(max(data[y][x],bottom+0.1),maxz)
                     ]
                 ]
             ] : [
diff --git a/skin.scad b/skin.scad
index c864735..00a151e 100644
--- a/skin.scad
+++ b/skin.scad
@@ -21,7 +21,7 @@
 // Synopsis: Connect a sequence of arbitrary polygons into a 3D object. 
 // SynTags: VNF, Geom
 // Topics: Extrusion, Skin
-// See Also: sweep(), linear_sweep(), rotate_sweep(), spiral_sweep(), path_sweep(), offset_sweep()
+// See Also: vnf_vertex_array(), sweep(), linear_sweep(), rotate_sweep(), spiral_sweep(), path_sweep(), offset_sweep()
 // Usage: As module:
 //   skin(profiles, slices, [z=], [refine=], [method=], [sampling=], [caps=], [closed=], [style=], [convexity=], [anchor=],[cp=],[spin=],[orient=],[atype=]) [ATTACHMENTS];
 // Usage: As function:
@@ -163,6 +163,8 @@
 //   atype = Select "hull" or "intersect" anchor types. Default: "hull"
 //   cp = Centerpoint for determining "intersect" anchors or centering the shape.  Determintes the base of the anchor vector.  Can be "centroid", "mean", "box" or a 3D point.  Default: "centroid"
 //   style = vnf_vertex_array style.  Default: "min_edge"
+// Named Anchors:
+//   "origin" = The native position of the shape.  
 // Anchor Types:
 //   "hull" = Anchors to the virtual convex hull of the shape.
 //   "intersect" = Anchors to the surface of the shape.
@@ -562,7 +564,7 @@ function skin(profiles, slices, refine=1, method="direct", sampling, caps, close
 //   "hull" = Anchors to the virtual convex hull of the shape.
 //   "intersect" = Anchors to the surface of the shape.
 //   "bbox" = Anchors to the bounding box of the extruded shape.
-// Extra Anchors:
+// Named Anchors:
 //   "origin" = Centers the extruded shape vertically only, but keeps the original path positions in the X and Y.  Oriented UP.
 //   "original_base" = Keeps the original path positions in the X and Y, but at the bottom of the extrusion.  Oriented UP.
 // Example: Extruding a Compound Region.
@@ -884,6 +886,8 @@ function linear_sweep(
 //   anchor = Translate so anchor point is at the origin. Default: "origin"
 //   spin = Rotate this many degrees around Z axis after anchor. Default: 0
 //   orient = Vector to rotate top towards after spin  (module only)
+// Named Anchors:
+//   "origin" = The native position of the shape.  
 // Anchor Types:
 //   "hull" = Anchors to the virtual convex hull of the shape.
 //   "intersect" = Anchors to the surface of the shape.
@@ -1492,11 +1496,12 @@ module spiral_sweep(poly, h, r, turns=1, taper, r1, r2, d, d1, d2, internal=fals
 // Anchor Types:
 //   "hull" = Anchors to the virtual convex hull of the shape.
 //   "intersect" = Anchors to the surface of the shape.
-// Extra Anchors:
-//   start = When `closed==false`, the origin point of the shape, on the starting face of the object
-//   end = When `closed==false`, the origin point of the shape, on the ending face of the object
-//   start-centroid = When `closed==false`, the centroid of the shape, on the starting face of the object
-//   end-centroid = When `closed==false`, the centroid of the shape, on the ending face of the object
+// Named Anchors:
+//   "origin" = The native position of the shape
+//   "start" = When `closed==false`, the origin point of the shape, on the starting face of the object
+//   "end" = When `closed==false`, the origin point of the shape, on the ending face of the object
+//   "start-centroid" = When `closed==false`, the centroid of the shape, on the starting face of the object
+//   "end-centroid" = When `closed==false`, the centroid of the shape, on the ending face of the object
 // Example(NoScales): A simple sweep of a square along a sine wave:
 //   path = [for(theta=[-180:5:180]) [theta/10, 10*sin(theta)]];
 //   sq = square(6,center=true);
@@ -1800,11 +1805,14 @@ module path_sweep(shape, path, method="incremental", normal, closed, twist=0, tw
             assert(in_list(atype, _ANCHOR_TYPES), "Anchor type must be \"hull\" or \"intersect\"");
     trans_scale = path_sweep(shape, path, method, normal, closed, twist, twist_by_length, scale, scale_by_length,
                             symmetry, last_normal, tangent, uniform, relaxed, caps, style, transforms=true,_return_scales=true);
+    caps = is_def(caps) ? caps :
+           closed ? false : true;
+    fullcaps = is_bool(caps) ? [caps,caps] : caps;
     transforms = trans_scale[0];
     scales = trans_scale[1];
     firstscale = is_num(scales[0]) ? 1/scales[0] : [1/scales[0].x, 1/scales[0].y];
     lastscale = is_num(last(scales)) ? 1/last(scales) : [1/last(scales).x, 1/last(scales).y];
-    vnf = sweep(is_path(shape)?clockwise_polygon(shape):shape, transforms, closed=false, caps=caps,style=style);
+    vnf = sweep(is_path(shape)?clockwise_polygon(shape):shape, transforms, closed=false, caps=fullcaps,style=style);
     shapecent = point3d(centroid(shape));
     $sweep_transforms = transforms;
     $sweep_scales = scales;
@@ -2037,6 +2045,8 @@ function path_sweep(shape, path, method="incremental", normal, closed, twist=0,
 //   orient = Vector to rotate top towards after spin
 //   atype = Select "hull" or "intersect" anchor types.  Default: "hull"
 //   cp = Centerpoint for determining "intersect" anchors or centering the shape.  Determintes the base of the anchor vector.  Can be "centroid", "mean", "box" or a 3D point.  Default: "centroid"
+// Named Anchors:
+//   "origin" = The native position of the shape.  
 // Anchor Types:
 //   "hull" = Anchors to the virtual convex hull of the shape.
 //   "intersect" = Anchors to the surface of the shape.
@@ -2168,6 +2178,8 @@ function _ofs_face_edge(face,firstlen,second=false) =
 //   anchor = Translate so anchor point is at the origin. Default: "origin"
 //   spin = Rotate this many degrees around Z axis after anchor. Default: 0
 //   orient = Vector to rotate top towards after spin  (module only)
+// Named Anchors:
+//   "origin" = The native position of the shape.  
 // Anchor Types:
 //   "hull" = Anchors to the virtual convex hull of the shape.
 //   "intersect" = Anchors to the surface of the shape.
@@ -3865,10 +3877,10 @@ function texture(tex, n, border, gap, roughness, inset) =
 ///   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `CENTER`
 ///   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
 ///   orient = Vector to rotate top towards, after spin.  See [orient](attachments.scad#subsection-orient).  Default: `UP`
-/// Extra Anchors:
-///   centroid_top = The centroid of the top of the shape, oriented UP.
-///   centroid = The centroid of the center of the shape, oriented UP.
-///   centroid_bot = The centroid of the bottom of the shape, oriented DOWN.
+/// Named Anchors:
+///   "centroid_top" = The centroid of the top of the shape, oriented UP.
+///   "centroid" = The centroid of the center of the shape, oriented UP.
+///   "centroid_bot" = The centroid of the bottom of the shape, oriented DOWN.
 
 function _get_vnf_tile_edges(texture) =
     let(
diff --git a/vnf.scad b/vnf.scad
index a2f7ab9..3ef2290 100644
--- a/vnf.scad
+++ b/vnf.scad
@@ -1063,7 +1063,7 @@ function _slice_3dpolygons(polys, dir, cuts) =
 // Anchor Types:
 //   "hull" = Anchors to the virtual convex hull of the shape.
 //   "intersect" = Anchors to the surface of the shape.
-// Extra Anchors:
+// Named Anchors:
 //   "origin" = Anchor at the origin, oriented UP.
 module vnf_polyhedron(vnf, convexity=2, cp="centroid", anchor="origin", spin=0, orient=UP, atype="hull") {
     vnf = is_vnf_list(vnf)? vnf_join(vnf) : vnf;
diff --git a/walls.scad b/walls.scad
index 1122559..c1748fe 100644
--- a/walls.scad
+++ b/walls.scad
@@ -9,6 +9,8 @@
 //////////////////////////////////////////////////////////////////////
 
 
+include<rounding.scad>
+
 // Section: Walls
 
 
@@ -16,7 +18,7 @@
 // Synopsis: Makes an open cross-braced rectangular wall.
 // SynTags: Geom
 // Topics: FDM Optimized, Walls
-// See Also: sparse_wall(), corrugated_wall(), thinning_wall(), thinning_triangle(), narrowing_strut()
+// See Also: corrugated_wall(), thinning_wall(), thinning_triangle(), narrowing_strut()
 //
 // Usage:
 //   sparse_wall(h, l, thick, [maxang=], [strut=], [max_bridge=]) [ATTACHMENTS];
@@ -30,9 +32,9 @@
 //   l = length of strut wall.
 //   thick = thickness of strut wall.
 //   ---
-//   maxang = maximum overhang angle of cross-braces.
-//   strut = the width of the cross-braces.
-//   max_bridge = maximum bridging distance between cross-braces.
+//   maxang = maximum overhang angle of cross-braces, measured down from vertical.  Default: 30 
+//   strut = the width of the cross-braces. Default: 5
+//   max_bridge = maximum bridging distance between cross-braces.  Default: 20
 //   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `CENTER`
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
 //   orient = Vector to rotate top towards, after spin.  See [orient](attachments.scad#subsection-orient).  Default: `UP`
@@ -129,7 +131,6 @@ module sparse_wall2d(size=[50,100], maxang=30, strut=5, max_bridge=20, anchor=CE
 
     ang = atan(ystep/zstep);
     len = zstep / cos(ang);
-
     attachable(anchor,spin, two_d=true, size=size) {
         union() {
             difference() {
@@ -138,8 +139,8 @@ module sparse_wall2d(size=[50,100], maxang=30, strut=5, max_bridge=20, anchor=CE
             }
             ycopies(ystep, n=yreps) {
                 xcopies(zstep, n=zreps) {
-                    skew(syx=tan(-ang)) square([(h-strut)/zreps, strut], center=true);
-                    skew(syx=tan( ang)) square([(h-strut)/zreps, strut], center=true);
+                    skew(syx=tan(-ang)) square([(h-strut)/zreps, strut/cos(ang)], center=true);
+                    skew(syx=tan( ang)) square([(h-strut)/zreps, strut/cos(ang)], center=true);
                 }
             }
         }
@@ -148,6 +149,303 @@ module sparse_wall2d(size=[50,100], maxang=30, strut=5, max_bridge=20, anchor=CE
 }
 
 
+// Module: sparse_cuboid()
+// Synopsis: Makes an open cross-braced cuboid
+// SynTags: Geom
+// Topics: FDM Optimized, Walls
+// See Also: sparse_wall(), corrugated_wall(), thinning_wall(), thinning_triangle(), narrowing_strut(), cuboid()
+// Usage:
+//   sparse_cuboid(size, [dir], [maxang=], [struct=]
+// Description:
+//   Makes an open rectangular cuboid with X-shaped cross-bracing to reduce the need for material in 3d printing.
+//   The direction of the cross bracing can be aligned with the X, Y or Z axis.  This module can be
+//   used as a drop-in replacement for {{cuboid()}} if you belatedly decide that your model would benefit from
+//   the sparse construction.  Note that for Z aligned bracing the max_bridge parameter contrains the gaps that are parallel
+//   to the Y axis, and the angle is measured relative to the X direction.  
+// Arguments:
+//   size = The size of sparse wall, a number or length 3 vector.
+//   dir = direction of holes through the cuboid, must be a vector parallel to the X, Y or Z axes, or one of "X", "Y" or "Z".  Default: "Y"
+//   ---
+//   maxang = maximum overhang angle of cross-braces, measured down from vertical.  Default: 30 
+//   strut = the width of the cross-braces. Default: 5
+//   max_bridge = maximum bridging distance between cross-braces.  Default: 20
+//   chamfer = Size of chamfer, inset from sides.  Default: No chamfering.
+//   rounding = Radius of the edge rounding.  Default: No rounding.
+//   edges = Edges to mask.  See [Specifying Edges](attachments.scad#section-specifying-edges).  Default: all edges.
+//   except = Edges to explicitly NOT mask.  See [Specifying Edges](attachments.scad#section-specifying-edges).  Default: No edges.
+//   trimcorners = If true, rounds or chamfers corners where three chamfered/rounded edges meet.  Default: `true`
+//   teardrop = If given as a number, rounding around the bottom edge of the cuboid won't exceed this many degrees from vertical.  If true, the limit angle is 45 degrees.  Default: `false`
+//   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `CENTER`
+//   spin = Rotate this many degrees around the Z axis.  See [spin](attachments.scad#subsection-spin).  Default: `0`
+//   orient = Vector to rotate top towards.  See [orient](attachments.scad#subsection-orient).  Default: `UP`
+// Examples:
+//   sparse_cuboid([10,20,30], strut=1);
+//   sparse_cuboid([10,20,30], "Y", strut=1);
+//   sparse_cuboid([10,20,30], UP, strut=1);
+//   sparse_cuboid(30, FWD, strut=2, rounding=2, $fn=24);
+module sparse_cuboid(size, dir=RIGHT, strut=5, maxang=30, max_bridge=20,
+    chamfer,
+    rounding,
+    edges=EDGES_ALL,
+    except=[],
+    except_edges,
+    trimcorners=true,
+    teardrop=false,
+    anchor=CENTER, spin=0, orient=UP)
+{
+  size = scalar_vec3(size);
+  dummy1=assert(in_list(dir,["X","Y","Z"]) || is_vector(dir,3), "dir must be a 3-vector or one of \"X\", \"Y\", or \"Z\"");
+  count = len([for(d=dir) if (d!=0) d]);
+  dummy2=assert(is_string(dir) || (count==1 && len(dir)<=3), "vector valued dir must have exactly one non-zero component");
+  dir = is_string(dir) ? dir
+      : dir.x ? "X"
+      : dir.y ? "Y"
+      : "Z";
+  attachable(anchor,spin,orient,size=size){
+    intersection(){
+      if (dir=="X")
+         sparse_wall(size.z,size.y,size.x,strut=strut,maxang=maxang, max_bridge=max_bridge);
+      else if (dir=="Y")
+         zrot(90)
+           sparse_wall(size.z,size.x,size.y,strut=strut,maxang=maxang, max_bridge=max_bridge);
+      else
+         yrot(90)
+           sparse_wall(size.x,size.y,size.z,strut=strut,maxang=maxang, max_bridge=max_bridge);
+      cuboid(size=size, chamfer=chamfer, rounding=rounding,edges=edges, except=except, except_edges=except_edges,
+           trimcorners=trimcorners, teardrop=teardrop);
+    }
+    children();
+  }    
+}
+
+
+// Module: hex_panel()
+// Usage:
+//   hex_panel(shape, wall, spacing, [frame=], [bevel=], [bevel_frame=], [h=|height=|l=|length=], [anchor=], [orient=], [spin=])
+// Description:
+//   Produces a panel with a honeycomb interior. The panel consists of a frame containing
+//   a honeycob interior. The frame is laid out in the XY plane with the honeycob interior 
+//   and then extruded to the height h. The shape argument defines the outer bounderies of
+//   the frame.
+//   .
+//   The simplest way to define the frame shape is to give a cuboid size as a 3d vector for
+//   the shape argument.  The h argument is not allowed in this case.  With rectangular frames you can supply the
+//   bevel argument which applies a 45 deg bevel on the specified list of edges.  These edges
+//   can be LEFT, RIGHT, FRONT, or BACK to place a bevel the edge facing upward.  You can add
+//   BOTTOM, as in LEFT+BOT, to get a bevel that faces down.  When beveling a separate beveled frame
+//   is added to the model.  You can independently control its thickness by setting `bevel_frame`, which
+//   defaults to the frame thickness.  Note also that `frame` and `bevel_frame` can be set to zero
+//   to produce just the honeycomb.  
+//   . 
+//   The other option is to provide a 2D path as the shape argument. The path must not intersect
+//   itself.  You must give the height argument in this case and you cannot give the bevel argument.
+//   The panel is made from a linear extrusion of the specified shape.  In this case, anchoring
+//   is done as usual for linear sweeps.  The shape appears by default on its base and you can
+//   choose "hull" or "intersect" anchor types.  
+// Arguments:
+//   shape = 3D size vector or a 2D path
+//   strut = thickness of hexagonal bracing
+//   spacing = center-to-center spacing of hex cells in the honeycomb.
+//   --
+//   frame = width of the frame around the honeycomb.  Default: same as strut
+//   bevel = list of edges to bevel on rectangular case when shape is a size vector; allowed options are RIGHT, LEFT, BACK, or FRONT, or those directions with BOTTOM added.  Default: []
+//   bevel_frame = width of the frame applied at bevels.  Default: same as frame
+//   h / height / l / length = thickness of the panel when shape is a path 
+//   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `CENTER` for rectangular panels, `"zcenter"` for extrusions.  
+//   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`
+//   orient = Vector to rotate top towards, after spin.  See [orient](attachments.scad#subsection-orient).  Default: `UP`
+//   atype = Select "hull", "intersect" anchor types.  Default: "hull"
+//   cp = Centerpoint for determining "intersect" anchors or centering the shape.  Determintes the base of the anchor vector.  Can be "centroid", "mean", "box" or a 3D point.  Default: "centroid"
+// Named Anchors:
+//   "base" = Anchor to the base of the shape in its native position
+//   "top" = Anchor to the top of the shape in its native position
+//   "zcenter" = Center shape in the Z direction in the native XY position (default)
+// Anchor Types:
+//   hull = Anchors to the convex hull of the linear sweep of the path, ignoring any end roundings. 
+//   intersect = Anchors to the surface of the linear sweep of the path, ignoring any end roundings.
+// Examples
+//     hex_panel([50, 100, 5], strut=1.5, spacing=10);
+//     hex_panel([50, 100, 5], 1.5, 10, frame = 5);
+//     hex_panel([50, 100, 5], 5, 10.05);
+//     hex_panel([50, 100, 5], 1.5, 20, frame = 5);
+//     hex_panel([50, 100, 5], 1.5, 12, frame = 0);
+//     hex_panel([50, 100, 5], frame = 10, spacing = 20, strut = 4);
+//     hex_panel([50, 100, 10], 1.5, 10, frame = 5, bevel = [LEFT, RIGHT]);
+//     hex_panel([50, 100, 10], 1.5, 10, frame = 5, bevel = [FWD,  BACK]);
+//     hex_panel([50, 100, 10], 1.5, 10, frame = 3, bevel = [LEFT, RIGHT, FWD, BACK]);
+//     hex_panel([50, 100, 10], 1.5, 10, frame = 1, bevel = [LEFT, RIGHT, FWD+BOTTOM, BACK+BOTTOM]);
+//     hex_panel([50, 100, 10], 1.5, 10, frame=2, bevel_frame=0, bevel = [FWD, BACK+BOT, RIGHT, LEFT]);
+// Example: Triangle
+//     s = [[0, -40], [0, 40], [60, 0]];
+//     hex_panel(s, strut=1.5, spacing=10, h = 10, frame = 5); 
+// Example: Concave polygon
+//     s = [[0, -40], [0, 70], [60, 0], [80, 20], [70, -20]];
+//     hex_panel(s, 1.5, 10, h = 10, frame = 5); 
+// Example: Another concave example
+//     s = [[0, -40], [0, 40], [30, 20], [60, 40], [60, -40], [30, -20]];
+//     hex_panel(s, 1.5, 10, h = 10, frame = 5); 
+// Example: Circular panel
+//     hex_panel(circle(30), 1.5, 10, h = 10, frame = 5);
+// Example: More complicated shape
+//     s = glued_circles(d=50, spread=50, tangent=30);
+//     hex_panel(s, 1.5, 10, h = 10, frame = 5);
+// Example: Care is required when arranging panels vertically for 3d printability.  Setting `orient=RIGHT` produces the correct result. 
+//     hex_panel([50, 100, 10], 1.5, 10, frame = 5, bevel = [FWD, BACK], anchor = BACK + RIGHT + BOTTOM, orient = RIGHT);
+//     zrot(-90)hex_panel([50, 100, 10], 1.5, 10, frame = 5,  bevel = [FWD, BACK], anchor = FWD + RIGHT + BOTTOM, orient = RIGHT);
+// Example: In this example panels one of the panels is positioned with `orient=FWD` which produces hexagons with 60 deg overhang edges that may not be 3d printable.  This example alsu uses `bevel_frame` to thin the material at the corner.  
+//     hex_panel([50, 100, 10], 1.5, 10, frame = 5, bevel_frame=1, bevel = [FWD,  BACK], anchor = BACK + RIGHT + BOTTOM, orient = RIGHT);
+//     hex_panel([100, 50, 10], 1.5, 10, frame = 5, bevel_frame=1, bevel = [LEFT, RIGHT], anchor = FWD + LEFT + BOTTOM, orient = FWD);
+// Example: Joining panels with {{attach()}}.  In this case panels were joined front beveled edge to back beveled edge, which means the hex structure doesn't align at the joint
+//     hex_panel([50, 100, 10], 1.5, 10, frame = 5, bevel_frame=0, bevel = [FWD, BACK], anchor = BACK + RIGHT + BOTTOM, orient = RIGHT)
+//       attach(BACK,FRONT) 
+//          hex_panel([50, 100, 10], 1.5, 10, frame = 5, bevel_frame=0, bevel = [FWD, BACK]);
+// Example: Joining panels with {{attach()}}.  Attaching BACK to BACK aligns the hex structure which looks better.  
+//     hex_panel([50, 100, 10], 1.5, 10, frame = 1, bevel = [FWD, BACK], anchor = BACK + RIGHT + BOTTOM, orient = RIGHT)
+//       attach(BACK,BACK) 
+//          hex_panel([50, 100, 10], 1.5, 10, frame = 1, bevel = [FWD, BACK]);
+module hex_panel(
+    shape,
+    strut,
+    spacing,
+    frame,
+    bevel_frame,
+    h, height, l, length, 
+    bevel = [],
+    anchor, 
+    orient = UP, cp="centroid", atype="hull",
+    spin = 0) 
+{
+    frame = first_defined([frame,strut]);
+    bevel_frame = first_defined([bevel_frame, frame]);
+    shape = force_path(shape,"shape");
+    bevel = is_vector(bevel) ? [bevel] : bevel;
+    bevOK = len([for(bev=bevel) if (norm([bev.x,bev.y])==1 && (bev.x==0 || bev.y==0) && (bev.z==0 || bev.z==-1)) 1]) == len(bevel);
+    dummy=
+      assert(is_finite(strut) && strut > 0, "strut must be positive")
+      assert(is_finite(frame) && frame >= 0, "frame must be nonnegative")
+      assert(is_finite(bevel_frame) && bevel_frame >= 0, "bevel_frame must be nonnegative")
+      assert(is_finite(spacing) && spacing>0, "spacing must be positive")
+      assert(is_path(shape,2) || is_vector(shape, 3), "shape must be a path or a 3D vector")
+      assert(len(bevel) == 0 || is_vector(shape, 3), "bevel must be used only on rectangular panels")
+      assert(is_path(shape) || all_positive(shape), "when shape is a size vector all components must be positive")
+      assert(bevOK, "bevel list contains an invalid entry")
+      assert(!(in_list(FRONT, bevel) && in_list(FRONT+BOTTOM, bevel)), "conflicting FRONT bevels")
+      assert(!(in_list(BACK,  bevel) && in_list(BACK+BOTTOM,  bevel)), "conflicting BACK bevels")
+      assert(!(in_list(RIGHT, bevel) && in_list(RIGHT+BOTTOM, bevel)), "conflicting RIGHT bevels")
+      assert(!(in_list(LEFT,  bevel) && in_list(LEFT+BOTTOM,  bevel)), "conflicting LEFT bevels")
+      assert(is_undef(h) || is_path(shape), "cannot give h with a size vector");
+    shp = is_path(shape) ? shape : square([shape.x, shape.y], center = true);
+    ht = is_path(shape) ? one_defined([h,l,height,length],"height,length,l,h")
+       : shape.z;
+    
+    bounds = pointlist_bounds(shp);
+    sizes = bounds[1] - bounds[0]; // [xsize, ysize]
+    assert(frame*2 + spacing < sizes[0], "There must be room for at least 1 cell in the honeycomb");
+    assert(frame*2 + spacing < sizes[1], "There must be room for at least 1 cell in the honeycomb");
+
+    bevpaths = len(bevel)==0 ? []
+             : _bevelSolid(shape,bevel);
+    if (len(bevel) > 0) {
+         size1 = [bevpaths[0][0].x-bevpaths[0][1].x, bevpaths[0][2].y-bevpaths[0][1].y,ht];
+         size2 = [bevpaths[1][0].x-bevpaths[1][1].x, bevpaths[1][2].y-bevpaths[1][1].y];
+         shift = point2d(centroid(bevpaths[1])-centroid(bevpaths[0]));
+         offset = (centroid(bevpaths[0]));
+         attachable(anchor,spin,orient,size=size1,size2=size2,shift=shift,offset=offset){
+             down(ht/2)
+                 intersection() {
+                     union() {
+                         linear_extrude(height = ht, convexity=8) {
+                             _honeycomb(shp, spacing = spacing, hex_wall = strut);
+                             offset_stroke(shp, width=[-frame, 0], closed=true);
+                         }
+                         for (b = bevel) _bevelWall(shape, b, bevel_frame);
+                     }
+                     vnf_polyhedron(vnf_vertex_array(bevpaths, col_wrap=true, caps=true));
+                 }
+             children();
+         }
+     }
+     else if (is_vector(shape)){
+         attachable(anchor = anchor, spin = spin, orient = orient, size = shape) {        
+             down(ht/2) 
+                 linear_extrude(height = ht, convexity=8) {
+                     _honeycomb(shp, spacing = spacing, hex_wall = strut);
+                     offset_stroke(shp, width=[-frame, 0], closed=true);
+                 }
+             children();
+         }
+    }
+    else {
+         anchors = [
+           named_anchor("zcenter", [0,0,0], UP),
+           named_anchor("base", [0,0,-ht/2], UP),
+           named_anchor("top", [0,0,ht/2], UP)          
+         ];
+         attachable(anchor = default(anchor,"zcenter"), spin = spin, orient = orient, path=shp, h=ht, cp=cp, extent=atype=="hull",anchors=anchors) {        
+              down(ht/2) 
+                 linear_extrude(height = ht, convexity=8) {
+                     _honeycomb(shp, spacing = spacing, hex_wall = strut);
+                     offset_stroke(shp, width=[-frame, 0], closed=true);
+                 }
+             children();
+         }
+
+    } 
+}
+
+
+module _honeycomb(shape, spacing=10, hex_wall=1) 
+{
+        hex = hexagon(id=spacing-hex_wall, spin=180/6);
+        bounds = pointlist_bounds(shape);
+        size = bounds[1] - bounds[0];
+        hex_rgn2 = grid_copies(spacing=spacing, size=size, stagger=true, p=hex);
+        center = (bounds[0] + bounds[1]) / 2;
+        hex_rgn = move(center, p=hex_rgn2);
+        difference(){
+            polygon(shape);
+            region(hex_rgn);
+        }
+}
+
+
+function _bevelSolid(shape, bevel) =
+  let(
+    tX = in_list(RIGHT,          bevel) ? -shape.z : 0,
+    tx = in_list(LEFT,           bevel) ?  shape.z : 0,
+    tY = in_list(BACK,           bevel) ? -shape.z : 0,
+    ty = in_list(FRONT,          bevel) ?  shape.z : 0,
+    bX = in_list(RIGHT + BOTTOM, bevel) ? -shape.z : 0,
+    bx = in_list(LEFT  + BOTTOM, bevel) ?  shape.z : 0,
+    bY = in_list(BACK  + BOTTOM, bevel) ? -shape.z : 0,
+    by = in_list(FRONT + BOTTOM, bevel) ?  shape.z : 0,
+    pathB = path3d(rect(select(shape,0,1)) + [[bX,by],[bx,by],[bx,bY],[bX,bY]]),
+    pathT = path3d(rect(select(shape,0,1)) + [[tX,ty],[tx,ty],[tx,tY],[tX,tY]],shape.z)
+  )
+  [pathB,pathT];
+
+module _bevelWall(shape, bevel, thickness) {
+
+    l = bevel.y != 0 ? shape.x : shape.y;
+    d = bevel.y != 0 ? shape.y : shape.x;
+    zr = bevel.y == -1 ? 180 
+       : bevel.y ==  1 ? 0 
+       : bevel.x == -1 ? 90 
+       : bevel.x ==  1 ? 270 
+       : undef;
+    xr = bevel.x != 0 && bevel.z < 0 ? 180 : 0;
+    yr = bevel.y != 0 && bevel.z < 0 ? 180 : 0;
+    
+    path = [[-thickness, 0], [0, 0], [-shape.z, -shape.z], [-shape.z-thickness, -shape.z]];
+
+    up(shape.z/2)
+    xrot(xr) yrot(yr) zrot(zr) down(shape.z/2)
+      back(d/2) right(l/2) 
+      zrot(90) xrot(-90)
+        linear_extrude(l) polygon(path);
+}
+
+
 // Module: corrugated_wall()
 // Synopsis: Makes a corrugated rectangular wall.
 // SynTags: Geom
@@ -166,7 +464,7 @@ module sparse_wall2d(size=[50,100], maxang=30, strut=5, max_bridge=20, anchor=CE
 //   l = length of strut wall.
 //   thick = thickness of strut wall.
 //   ---
-//   strut = the width of the cross-braces.
+//   strut = the width of the frame.
 //   wall = thickness of corrugations.
 //   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#subsection-anchor).  Default: `CENTER`
 //   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#subsection-spin).  Default: `0`