diff --git a/ChangeLog.md b/ChangeLog.md
index 1f5f511b..f9f9e351 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,3 +1,13 @@
+# Changes in 1.2.1
+
+## New draft extensions
+
+* [undo.h](include/clap/ext/draft/undo.h): shared undo stack for the host and plugin.
+
+## Documentation
+
+* [events.h](include/clap/events.h): clarification for note on events.
+
 # Changes in 1.2.0
 
 ## New conventions
diff --git a/include/clap/all.h b/include/clap/all.h
index 45412475..2ce982a5 100644
--- a/include/clap/all.h
+++ b/include/clap/all.h
@@ -10,3 +10,4 @@
 #include "ext/draft/transport-control.h"
 #include "ext/draft/triggers.h"
 #include "ext/draft/tuning.h"
+#include "ext/draft/undo.h"
diff --git a/include/clap/events.h b/include/clap/events.h
index 5086b4df..a6e97513 100644
--- a/include/clap/events.h
+++ b/include/clap/events.h
@@ -144,6 +144,12 @@ enum {
 // Well constructed plugins will search for voices and notes using
 // the entire tuple.
 //
+// In the case of note on events:
+// - The port, channel and key must be specified with a value >= 0
+// - A note-on event with a '-1' for port, channel or key is invalid and
+//   can be rejected or ignored by a plugin or host.
+// - A host which does not support note ids should set the note id to -1.
+//
 // In the case of note choke or end events:
 // - the velocity is ignored.
 // - key and channel are used to match active notes
diff --git a/include/clap/ext/draft/undo.h b/include/clap/ext/draft/undo.h
new file mode 100644
index 00000000..365780e6
--- /dev/null
+++ b/include/clap/ext/draft/undo.h
@@ -0,0 +1,163 @@
+#pragma once
+
+#include "../../plugin.h"
+
+static CLAP_CONSTEXPR const char CLAP_EXT_UNDO[] = "clap.undo/2";
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/// @page Undo
+///
+/// This extension enables the plugin to merge its undo history with the host.
+/// This leads to a single undo history shared by the host and many plugins.
+///
+/// Calling host->undo() or host->redo() is equivalent to clicking undo/redo within the host's GUI.
+///
+/// If the plugin implements this interface then its undo and redo should be entirely delegated to
+/// the host; clicking in the plugin's UI undo or redo is equivalent to clicking undo or redo in the
+/// host's UI.
+///
+/// Some changes are long running changes, for example a mouse interaction will begin editing some
+/// complex data and it may take multiple events and a long duration to complete the change.
+/// In such case the plugin will call host->begin_change() to indicate the beginning of a long
+/// running change and complete the change by calling host->change_made().
+///
+/// The host may group changes together:
+/// [---------------------------------]
+/// ^-T0      ^-T1    ^-T2            ^-T3
+/// Here a long running change C0 begin at T0.
+/// A instantaneous change C1 at T1, and another one C2 at T2.
+/// Then at T3 the long running change is completed.
+/// The host will then create a single undo step that will merge all the changes into C0.
+///
+/// This leads to another important consideration: starting a long running change without
+/// terminating is **VERY BAD**, because while a change is running it is impossible to call undo or
+/// redo.
+///
+/// Rationale: multiple designs were considered and this one has the benefit of having a single undo
+/// history. This simplifies the host implementation, leading to less bugs, a more robust design
+/// and maybe an easier experience for the user because there's a single undo context versus one
+/// for the host and one for each plugin instance.
+
+enum clap_undo_context_flags {
+   // While the host is within a change, it is impossible to perform undo or redo.
+   CLAP_UNDO_IS_WITHIN_CHANGE = 1 << 0,
+};
+
+enum clap_undo_delta_properties_flags {
+   // If not set, then all clap_undo_delta_properties's attributes become irrelevant.
+   // If set, then the plugin will provide deltas in host->change_made().
+   CLAP_UNDO_DELTA_PROPERTIES_HAS_DELTA = 1 << 0,
+
+   // If set, then the delta will be reusable in the future as long as the plugin is
+   // compatible with the given format_version.
+   CLAP_UNDO_DELTA_PROPERTIES_IS_PERSISTENT = 1 << 1,
+};
+
+typedef struct clap_undo_delta_properties {
+   // Bitmask of clap_undo_delta_properties_flags
+   uint64_t flags;
+
+   // This represents the delta format version that the plugin is using.
+   uint32_t format_version;
+} clap_undo_delta_properties_t;
+
+typedef struct clap_plugin_undo {
+   // Asks the plugin the delta properties.
+   // [main-thread]
+   void(CLAP_ABI *get_delta_properties)(const clap_plugin_t          *plugin,
+                                        clap_undo_delta_properties_t *properties);
+
+   // Asks the plugin if it can apply a delta using the given format version.
+   // Returns true if it is possible.
+   // [main-thread]
+   bool(CLAP_ABI *can_use_delta_format_version)(const clap_plugin_t *plugin,
+                                                clap_id              format_version);
+
+   // Applies synchronously a delta.
+   // Returns true on success.
+   //
+   // [main-thread]
+   bool(CLAP_ABI *apply_delta)(const clap_plugin_t *plugin,
+                               clap_id              format_version,
+                               const void          *delta,
+                               size_t               delta_size);
+
+   // Sets the undo context.
+   // flags: bitmask of clap_undo_context_flags values
+   // names: null terminated string if an redo/undo step exists, null otherwise.
+   // [main-thread]
+   void(CLAP_ABI *set_context_info)(const clap_plugin_t *plugin,
+                                    uint64_t             flags,
+                                    const char          *undo_name,
+                                    const char          *redo_name);
+} clap_plugin_undo_t;
+
+typedef struct clap_host_undo {
+   // Begins a long running change.
+   // The plugin must not call this twice: there must be either a call to cancel_change() or
+   // change_made() before calling begin_change() again.
+   // [main-thread]
+   void(CLAP_ABI *begin_change)(const clap_host_t *host);
+
+   // Cancels a long running change.
+   // cancel_change() must not be called without a preceding begin_change().
+   // [main-thread]
+   void(CLAP_ABI *cancel_change)(const clap_host_t *host);
+
+   // Completes an undoable change.
+   // At the moment of this function call, plugin_state->save() would include the current change.
+   //
+   // name: mandatory null terminated string describing the change, this is displayed to the user
+   //
+   // deltas: optional, they are binary blobs used to perform the undo and redo. When not available
+   // the host will save the plugin state and use state->load() to perform undo and redo.
+   //
+   // Note: the provided delta may be used for incremental state saving and crash recovery. The
+   // plugin can indicate a format version id and the validity lifetime for the binary blobs.
+   // The host can use these to verify the compatibility before applying the delta.
+   // If the plugin is unable to use a delta, a notification should be provided to the user and
+   // the crash recovery should perform a best effort job, at least restoring the latest saved state.
+   //
+   // Special case: for objects with shared and synchronized state, changes shouldn't be reported
+   // as the host already knows about it.
+   // For example, plugin parameter changes shouldn't produce a call to change_made().
+   //
+   // [main-thread]
+   void(CLAP_ABI *change_made)(const clap_host_t *host,
+                               const char        *name,
+                               const void        *redo_delta,
+                               size_t             redo_delta_size,
+                               const void        *undo_delta,
+                               size_t             undo_delta_size);
+
+   // Asks the host to perform the next undo step.
+   // This operation may be asynchronous.
+   // [main-thread]
+   void(CLAP_ABI *undo)(const clap_host_t *host);
+
+   // Asks the host to perform the next redo step.
+   // This operation may be asynchronous.
+   // [main-thread]
+   void(CLAP_ABI *redo)(const clap_host_t *host);
+
+   // Subscribes to or unsubscribes from undo context info.
+   //
+   // This method helps reducing the number of calls the host has to perform when updating
+   // the undo context info. Consider a large project with 1000+ plugins, we don't want to
+   // call 1000+ times update, while the plugin may only need the context info if its GUI
+   // is shown and it wants to display undo/redo info.
+   //
+   // Initial state is unsubscribed.
+   //
+   // is_subscribed: set to true to receive context info
+   //
+   // [main-thread]
+   void(CLAP_ABI *set_context_info_subscription)(const clap_host_t *host, bool is_subscribed);
+} clap_host_undo_t;
+
+#ifdef __cplusplus
+}
+#endif
diff --git a/include/clap/version.h b/include/clap/version.h
index 6a3e782c..fdbd03a7 100644
--- a/include/clap/version.h
+++ b/include/clap/version.h
@@ -22,7 +22,7 @@ typedef struct clap_version {
 
 #define CLAP_VERSION_MAJOR 1
 #define CLAP_VERSION_MINOR 2
-#define CLAP_VERSION_REVISION 0
+#define CLAP_VERSION_REVISION 1
 
 #define CLAP_VERSION_INIT                                                                          \
    { (uint32_t)CLAP_VERSION_MAJOR, (uint32_t)CLAP_VERSION_MINOR, (uint32_t)CLAP_VERSION_REVISION }