Test case comments

tests/data/scad/3D/misc/polyhedron-self-touch-edge-nonmanifold.scad

@@ -1,3 +1,5 @@
+// A single volume touching itself (two pairs of coincident vertices forming an edge).
+// This is a non-manifold object since the collapsed vertices are not distinct.
 polyhedron(
   points=[
     [0, 0, 0],

tests/data/scad/3D/misc/polyhedron-self-touch-edge.scad

@@ -1,3 +1,5 @@
+// A single volume touching itself (two pairs of coincident vertices forming an edge),
+// but with a manifold topology (the coincident vertices are distinct).
 polyhedron(
   points=[
     [0, 0, 0],

tests/data/scad/3D/misc/polyhedron-self-touch-face.scad

@@ -1,3 +1,4 @@
+// A single volume touching itself (three pairs of coincident vertices forming a triangle).
 polyhedron(
   points=[
     [0, 0, 0],

tests/data/scad/3D/misc/polyhedrons-touch-edge-nonmanifold.scad

@@ -1,3 +1,5 @@
+// Two cubes sharing an edge.
+// This is a non-manifold object since the collapsed vertices are not distinct.
 polyhedron(
   points=[
     [0, 0, 0],

tests/data/scad/3D/misc/polyhedrons-touch-face.scad

@@ -1,3 +1,5 @@
+// Two cubes sharing a face,
+// but with a manifold topology (the coincident vertices are distinct).
 polyhedron(
   points=[
     [0, 0, 0],

tests/data/scad/3D/misc/polyhedrons-touch-vertex-nonmanifold.scad

@@ -1,3 +1,5 @@
+// Two cubes sharing a vertex.
+// This is a non-manifold object since the collapsed vertices are not distinct.
 polyhedron(
   points=[
     [0, 0, 0],

tests/data/scad/3D/misc/polyhedrons-touch-vertex.scad

@@ -1,3 +1,5 @@
+// Two cubes sharing a vertex,
+// but with a manifold topology (the coincident vertices are distinct).
 polyhedron(
   points=[
     [0, 0, 0],