+/**
+ * Represents a {@link ModificationApplyOperation} which is rooted at conceptual
+ * top of data tree.
+ *
+ * <p>
+ * This implementation differs from other implementations in this package that
+ * is not immutable, but may be upgraded to newer state if available by
+ * explicitly invoking {@link #upgradeIfPossible()} and also serves as factory
+ * for deriving snapshot {@link RootModificationApplyOperation} which will not
+ * be affected by upgrade of original one.
+ *
+ * <p>
+ * There are two variations of this {@link ModificationApplyOperation}:
+ * <ul>
+ * <li>
+ * <b>Upgradable</b> - operation may be upgraded to different backing
+ * implementation by invoking {@link #upgradeIfPossible()}.</li>
+ * <li><b>Not Upgradable</b> - operation is immutable, invocation of
+ * {@link #upgradeIfPossible()} is no-op and method {@link #snapshot()} returns
+ * pointer on same object.
+ *
+ * <h3>Upgradable Root Modification Operation</h3>
+ *
+ * Upgradable Root Modification Operation may be created using:
+ * <ul>
+ * <li> {@link #from(ModificationApplyOperation)} with other upgradable root
+ * modification as an argument
+ * <li>using factory {@link LatestOperationHolder} which instantiates Upgradable
+ * Root Modification Operations and provides an option to set latest
+ * implementation.
+ * </ul>
+ * <p>
+ * Upgradable root operation is never upgraded to latest operation
+ * automatically, but client code must explicitly invoke
+ * {@link #upgradeIfPossible()} to get latest implementation.
+ *
+ * Note: This is helpful for implementing
+ * {@link org.opendaylight.yangtools.yang.data.api.schema.tree.DataTreeModification}
+ * which may be derived from
+ * {@link org.opendaylight.yangtools.yang.data.api.schema.tree.DataTree} before
+ * update of schema and user actually writes data after schema update. During
+ * update user did not invoked any operation.
+ *
+ */
+abstract class RootModificationApplyOperation extends ModificationApplyOperation {