division_trace: add a comment about the transform method

my2to3/fixes/fix_division_trace.py

@@ -44,6 +44,15 @@ class FixDivisionTrace(BaseFix):
               if child.type == lib2to3.pgen2.token.SLASH]
 
   def transform(self, node, results):
+    # Transforming "a / b" into "division_traced(id, a, b) is fairly trivial.
+    # However, this is not the case when there are operations with the same
+    # priority as the division (i.e. division, multiplication) which are
+    # "in line", e.g.
+    # - "a / b / c"
+    # - "a * b / c * d / e"
+    # - ...
+    # That's why the logic is more complex here.
+
     previous_node = None
 
     for operator_pos in range(1, len(node.children), 2):