+ * Transaction may fail because of multiple reasons, such as
+ * <ul>
+ * <li>Another transaction finished earlier and modified the same node in
+ * non-compatible way (see below). In this case the returned future will fail with
+ * {@link OptimisticLockFailedException}. It is the responsibility of the
+ * caller to create a new transaction and submit the same modification again in
+ * order to update data tree.</li>
+ * <li>Data change introduced by this transaction did not pass validation by
+ * commit handlers or data was incorrectly structured. Returned future will
+ * fail with {@link DataValidationFailedException}. User should not retry to
+ * create new transaction with same data, since it probably will fail again.
+ * </li>
+ * </ul>
+ *
+ * <h3>Change compatibility</h3>
+ *
+ * There are several sets of changes which could be considered incompatible
+ * between two transactions which are derived from same initial state.
+ * Rules for conflict detection applies recursively for each subtree
+ * level.
+ *
+ * <h4>Change compatibility of leafs, leaf-list items</h4>
+ *
+ * Following table shows state changes and failures between two concurrent transactions,
+ * which are based on same initial state, Tx 1 completes successfully
+ * before Tx 2 is submitted.
+ *
+ * <table>
+ * <tr><th>Initial state</th><th>Tx 1</th><th>Tx 2</th><th>Result</th></tr>
+ * <tr><td>Empty</td><td>put(A,1)</td><td>put(A,2)</td><td>Tx 2 will fail, state is A=1</td></tr>
+ * <tr><td>Empty</td><td>put(A,1)</td><td>merge(A,2)</td><td>A=2</td></tr>
+ *
+ * <tr><td>Empty</td><td>merge(A,1)</td><td>put(A,2)</td><td>Tx 2 will fail, state is A=1</td></tr>
+ * <tr><td>Empty</td><td>merge(A,1)</td><td>merge(A,2)</td><td>A=2</td></tr>
+ *
+ *
+ * <tr><td>A=0</td><td>put(A,1)</td><td>put(A,2)</td><td>Tx 2 will fail, A=1</td></tr>
+ * <tr><td>A=0</td><td>put(A,1)</td><td>merge(A,2)</td><td>A=2</td></tr>
+ * <tr><td>A=0</td><td>merge(A,1)</td><td>put(A,2)</td><td>Tx 2 will fail, A=1</td></tr>
+ * <tr><td>A=0</td><td>merge(A,1)</td><td>merge(A,2)</td><td>A=2</td></tr>
+ *
+ * <tr><td>A=0</td><td>delete(A)</td><td>put(A,2)</td><td>Tx 2 will fail, A does not exists</td></tr>
+ * <tr><td>A=0</td><td>delete(A)</td><td>merge(A,2)</td><td>A=2</td></tr>
+ * </table>
+ *
+ * <h4>Change compatibility of subtrees</h4>
+ *
+ * Following table shows state changes and failures between two concurrent transactions,
+ * which are based on same initial state, Tx 1 completes successfully
+ * before Tx 2 is submitted.
+ *
+ * <table>
+ * <tr><th>Initial state</th><th>Tx 1</th><th>Tx 2</th><th>Result</th></tr>
+ *
+ * <tr><td>Empty</td><td>put(TOP,[])</td><td>put(TOP,[])</td><td>Tx 2 will fail, state is TOP=[]</td></tr>
+ * <tr><td>Empty</td><td>put(TOP,[])</td><td>merge(TOP,[])</td><td>TOP=[]</td></tr>
+ *
+ * <tr><td>Empty</td><td>put(TOP,[FOO=1])</td><td>put(TOP,[BAR=1])</td><td>Tx 2 will fail, state is TOP=[FOO=1]</td></tr>
+ * <tr><td>Empty</td><td>put(TOP,[FOO=1])</td><td>merge(TOP,[BAR=1])</td><td>TOP=[FOO=1,BAR=1]</td></tr>
+ *
+ * <tr><td>Empty</td><td>merge(TOP,[FOO=1])</td><td>put(TOP,[BAR=1])</td><td>Tx 2 will fail, state is TOP=[FOO=1]</td></tr>
+ * <tr><td>Empty</td><td>merge(TOP,[FOO=1])</td><td>merge(TOP,[BAR=1])</td><td>TOP=[FOO=1,BAR=1]</td></tr>
+ *
+ * <tr><td>TOP=[]</td><td>put(TOP,[FOO=1])</td><td>put(TOP,[BAR=1])</td><td>Tx 2 will fail, state is TOP=[FOO=1]</td></tr>
+ * <tr><td>TOP=[]</td><td>put(TOP,[FOO=1])</td><td>merge(TOP,[BAR=1])</td><td>state is TOP=[FOO=1,BAR=1]</td></tr>
+ * <tr><td>TOP=[]</td><td>merge(TOP,[FOO=1])</td><td>put(TOP,[BAR=1])</td><td>Tx 2 will fail, state is TOP=[FOO=1]</td></tr>
+ * <tr><td>TOP=[]</td><td>merge(TOP,[FOO=1])</td><td>merge(TOP,[BAR=1])</td><td>state is TOP=[FOO=1,BAR=1]</td></tr>
+ * <tr><td>TOP=[]</td><td>delete(TOP)</td><td>put(TOP,[BAR=1])</td><td>Tx 2 will fail, state is empty store</td></tr>
+ * <tr><td>TOP=[]</td><td>delete(TOP)</td><td>merge(TOP,[BAR=1])</td><td>state is TOP=[BAR=1]</td></tr>
+ *
+ * <tr><td>TOP=[]</td><td>put(TOP/FOO,1)</td><td>put(TOP/BAR,1])</td><td>state is TOP=[FOO=1,BAR=1]</td></tr>
+ * <tr><td>TOP=[]</td><td>put(TOP/FOO,1)</td><td>merge(TOP/BAR,1)</td><td>state is TOP=[FOO=1,BAR=1]</td></tr>
+ * <tr><td>TOP=[]</td><td>merge(TOP/FOO,1)</td><td>put(TOP/BAR,1)</td><td>state is TOP=[FOO=1,BAR=1]</td></tr>
+ * <tr><td>TOP=[]</td><td>merge(TOP/FOO,1)</td><td>merge(TOP/BAR,1)</td><td>state is TOP=[FOO=1,BAR=1]</td></tr>
+ * <tr><td>TOP=[]</td><td>delete(TOP)</td><td>put(TOP/BAR,1)</td><td>Tx 2 will fail, state is empty store</td></tr>
+ * <tr><td>TOP=[]</td><td>delete(TOP)</td><td>merge(TOP/BAR,1]</td><td>Tx 2 will fail, state is empty store</td></tr>
+ *
+ * <tr><td>TOP=[FOO=1]</td><td>put(TOP/FOO,2)</td><td>put(TOP/BAR,1)</td><td>state is TOP=[FOO=2,BAR=1]</td></tr>
+ * <tr><td>TOP=[FOO=1]</td><td>put(TOP/FOO,2)</td><td>merge(TOP/BAR,1)</td><td>state is TOP=[FOO=2,BAR=1]</td></tr>
+ * <tr><td>TOP=[FOO=1]</td><td>merge(TOP/FOO,2)</td><td>put(TOP/BAR,1)</td><td>state is TOP=[FOO=2,BAR=1]</td></tr>
+ * <tr><td>TOP=[FOO=1]</td><td>merge(TOP/FOO,2)</td><td>merge(TOP/BAR,1)</td><td>state is TOP=[FOO=2,BAR=1]</td></tr>
+ * <tr><td>TOP=[FOO=1]</td><td>delete(TOP/FOO)</td><td>put(TOP/BAR,1)</td><td>state is TOP=[BAR=1]</td></tr>
+ * <tr><td>TOP=[FOO=1]</td><td>delete(TOP/FOO)</td><td>merge(TOP/BAR,1]</td><td>state is TOP=[BAR=1]</td></tr>
+ * </table>
+ *
+ *
+ * <h3>Examples of failure scenarios</h3>
+ *
+ * <h4>Conflict of two transactions</h4>
+ *
+ * This example illustrates two concurrent transactions, which derived from
+ * same initial state of data tree and proposes conflicting modifications.
+ *
+ * <pre>
+ * txA = broker.newWriteTransaction(); // allocates new transaction, data tree is empty
+ * txB = broker.newWriteTransaction(); // allocates new transaction, data tree is empty
+ *
+ * txA.put(CONFIGURATION, PATH, A); // writes to PATH value A
+ * txB.put(CONFIGURATION, PATH, B) // writes to PATH value B
+ *
+ * ListenableFuture futureA = txA.commit(); // transaction A is sealed and committed
+ * ListenebleFuture futureB = txB.commit(); // transaction B is sealed and committed
+ * </pre>
+ *
+ * Commit of transaction A will be processed asynchronously and data tree
+ * will be updated to contain value <code>A</code> for <code>PATH</code>.
+ * Returned {@link ListenableFuture} will successfully complete once
+ * state is applied to data tree.
+ *
+ * Commit of Transaction B will fail, because previous transaction also
+ * modified path in a concurrent way. The state introduced by transaction B
+ * will not be applied. Returned {@link ListenableFuture} object will fail
+ * with {@link OptimisticLockFailedException} exception, which indicates to
+ * client that concurrent transaction prevented the submitted transaction from being
+ * applied.
+ *