doc fixes, allow threads=true with screw specs

distributors.scad

@@ -29,7 +29,7 @@
 //   then the `c` variable is set only in the scope of the `if` and `else` clauses and is not available later on when you actually
 //   try to use it.  Instead you must use the ternary operator and write:
 //   ```
-///  c = condition ? "red" : "green";
+//   c = condition ? "red" : "green";
 //   ```
 //   The second complication is
 //   that in OpenSCAD version 2021.01 and earlier, assignments in children were executed before their parent.  This means 

screws.scad

@@ -470,7 +470,7 @@ function _get_spec(spec, needtype, origin, thread,   // common parameters
                                            : nut_info(name,_origin=origin, thread=thread, shape=shape, thickness=thickness))
   : 
     assert(in_list(struct_val(spec,"type"), ["nut_info","screw_info"]), "Screw/nut spec is invalid struct type")
-    assert(is_undef(thread) || thread=="none" || thread==false || is_num(thread),
+    assert(is_undef(thread) || thread=="none" || thread==false || thread==true || is_num(thread),
            str("Thread type applied to struct specification must be numeric, \"none\" or false but got ",thread))
     assert(is_undef(thickness) || is_num(thickness), str("thickness applied to struct specification must be numeric but is ",thickness))
     assert(is_undef(head) || head=="none", str("The only head type allowed with struct specifications is \"none\" but got ",head))
@@ -483,7 +483,7 @@ function _get_spec(spec, needtype, origin, thread,   // common parameters
                                      if (head=="none") ["head","none"],
                                      if (head=="none") ["drive","none"],
                                      if (thread==false || thread=="none") ["pitch",0]
-                                     else ["pitch",thread],
+                                     else if (thread!=true) ["pitch",thread],
                                      ["thickness", thickness],
                                    ], grow=false)
     )
@@ -738,8 +738,8 @@ module screw(spec, head, drive, thread, drive_size,
 //   thread = thread type or specification for threaded masks, or false to make an unthreaded mask.  See [screw pitch](#subsection-standard-screw-pitch). Default: false
 //   teardrop = if true produce teardrop hole.  Only compatible with clearance holes, not threaded.  Default: false
 //   oversize = amount to increase diameter of all screw parts, a scalar or length 3 vector.  Default: 0
-//   oversize_hole = amount to increase diameter of the hole.
+//   hole_oversize = amount to increase diameter of the hole.
-//   oversize_head = amount to increase diameter of head.  
+//   head_oversize = amount to increase diameter of head.  
 //   length / l= length of screw (in mm)
 //   counterbore = set to length of counterbore, or true to make a counterbore equal to head height.  Default: false for flat heads and headless, true otherwise
 //   tolerance = threading or clearance hole tolerance.  For internal threads, detrmines actual thread geometry based on nominal sizing.  See [tolerance](#subsection-tolerance). Default is "2B" for UTS and 6H for ISO.  For clearance holes, determines how much clearance to add.  Default is "normal".  
@@ -810,6 +810,8 @@ module screw_hole(spec, head, thread, oversize, hole_oversize, head_oversize,
    if (threaded || is_def(oversize) || is_def(hole_oversize) || tolerance==0 || tolerance=="none") {
      undersize = is_def(oversize) ? -oversize
                : -[default(hole_oversize,0), default(head_oversize,0)];
+     echo_struct(spec);
+fdsa=     echo(undersize=undersize);
      default_tag("remove")
        screw(spec,head=head,thread=thread,undersize=undersize, higbee=higbee,
              length=length,l=l,thread_len=thread_len, tolerance=tolerance, _counterbore=counterbore,
@@ -1775,7 +1777,7 @@ module nut_trap_inline(length, spec, shape, l, height, h, nutwidth, anchor, orie
 //   ---
 //   thread = thread type or specification. See [screw pitch](#subsection-standard-screw-pitch). Default: "coarse"
 //   drive_size = size of drive recess to override computed value
-//   oversize = amount to increase screw diameter for clearance holes.  Default: 0
+//   threads_oversize = amount to increase screw diameter for clearance holes.  Default: 0
 //   head_oversize = amount to increase head diameter for countersink holes.  Default: 0 
 
 function screw_info(name, head, drive, thread, drive_size, threads_oversize=0, head_oversize=0, _origin) =

skin.scad

@@ -2691,13 +2691,13 @@ function associate_vertices(polygons, split, curpoly=0) =
 //       rect(30), texture=tex, h=30,
 //       tex_size=[10,10]
 //   );
-// Example(3D,VPR=[84.4,0,4.7]): **"checkers"** (VNF) = A pattern of alternating checkerboard squares.  Giving `inset=` specifies that the top face of the checker surface is smaller than the bottom by `inset` on each of the four sides.  As `inset` approaches 0.5 the tops come to sharp corners.  You must set `inset` strictly between 0 and 0.5.  Default: 0.05.
+// Example(3D,VPR=[84.4,0,4.7],VPT=[2.44496,6.53317,14.6135],VPD = 126): **"checkers"** (VNF) = A pattern of alternating checkerboard squares.  Giving `inset=` specifies that the top face of the checker surface is smaller than the bottom by `inset` on each of the four sides.  As `inset` approaches 0.5 the tops come to sharp corners.  You must set `inset` strictly between 0 and 0.5.  Default: 0.05.
 //   tex = texture("checkers");
 //   linear_sweep(
 //       rect(30), texture=tex, h=30,
 //       tex_size=[10,10]
 //   );
-// Example(3D,VPR=[76,0,24]): "checkers" texture with large inset.  
+// Example(3D,VPR=[84.4,0,4.7],VPT=[2.44496,6.53317,14.6135],VPD = 126): "checkers" texture with large inset.  
 //   tex = texture("checkers",inset=0.25);
 //   linear_sweep(
 //       rect(30), texture=tex, h=30,
@@ -2709,13 +2709,13 @@ function associate_vertices(polygons, split, curpoly=0) =
 //       rect(30), texture=tex, h=30, tex_scale=3,
 //       tex_size=[10,10]
 //   );
-// Example(3D): **"cubes"** (VNF) = Corner-cubes texture.  Note that this texture needs to be scaled in vertically by sqrt(3) to have its correct aspect
+// Example(3D): **"cubes"** (VNF) = Corner-cubes texture.  This texture needs to be scaled in vertically by sqrt(3) to have its correct aspect
 //   tex = texture("cubes");
 //   linear_sweep(
 //       rect(30), texture=tex, h=30,
 //       tex_size=[10,10]
 //   );
-// Example(3D): "cubes" texture at approximately the correct scale.  
+// Example(3D): "cubes" texture at the correct scale.  
 //   tex = texture("cubes");
 //   linear_sweep(
 //       rect(30), texture=tex, h=20*sqrt(3), tex_scale=3,