Merge branch 'bc/doc-merge-no-op-revert'

* bc/doc-merge-no-op-revert:
  Documentation: document pitfalls with 3-way merge

Author: gitster

Documentation/merge-strategies.txt

@@ -113,3 +113,11 @@ subtree::
 	match the tree structure of A, instead of reading the trees at
 	the same level. This adjustment is also done to the common
 	ancestor tree.
+
+With the strategies that use 3-way merge (including the default, 'recursive'),
+if a change is made on both branches, but later reverted on one of the
+branches, that change will be present in the merged result; some people find
+this behavior confusing.  It occurs because only the heads and the merge base
+are considered when performing a merge, not the individual commits.  The merge
+algorithm therefore considers the reverted change as no change at all, and
+substitutes the changed version instead.