+///
+/// Definition: A block is said to be forward statically reachable if there is
+/// a path from the entry of the function to the block. A statically reachable
+/// block may become statically unreachable during optimization.
+///
+/// A forward unreachable block may appear in the dominator tree, or it may
+/// not. If it does, dominance queries will return results as if all reachable
+/// blocks dominate it. When asking for a Node corresponding to a potentially
+/// unreachable block, calling code must handle the case where the block was
+/// unreachable and the result of getNode() is nullptr.
+///
+/// Generally, a block known to be unreachable when the dominator tree is
+/// constructed will not be in the tree. One which becomes unreachable after
+/// the dominator tree is initially constructed may still exist in the tree,
+/// even if the tree is properly updated. Calling code should not rely on the
+/// preceding statements; this is stated only to assist human understanding.