C++: QLDoc for Overlap in IR construction

cpp/ql/src/semmle/code/cpp/ir/internal/Overlap.qll

@@ -3,18 +3,33 @@ private newtype TOverlap =
   TMustTotallyOverlap() or
   TMustExactlyOverlap()
 
+/**
+ * Represents a possible overlap between two memory ranges.
+ */
 abstract class Overlap extends TOverlap {
   abstract string toString();
 }
 
+/**
+ * Represents a partial overlap between two memory ranges, which may or may not
+ * actually occur in practice.
+ */
 class MayPartiallyOverlap extends Overlap, TMayPartiallyOverlap {
   final override string toString() { result = "MayPartiallyOverlap" }
 }
 
+/**
+ * Represents an overlap in which the first memory range is known to include all
+ * bits of the second memory range, but may be larger or have a different type.
+ */
 class MustTotallyOverlap extends Overlap, TMustTotallyOverlap {
   final override string toString() { result = "MustTotallyOverlap" }
 }
 
+/**
+ * Represents an overlap between two memory ranges that have the same extent and
+ * the same type.
+ */
 class MustExactlyOverlap extends Overlap, TMustExactlyOverlap {
   final override string toString() { result = "MustExactlyOverlap" }
 }