Google protocol buffers .proto syntax for defining the MXP message structure:

package MXP;

message MVector3f {
required float X=1;
required float Y=2;
required float Z=3;
}

message MQuaternion4f {
required float X=1;
required float Y=2;
required float Z=3;
required float W=4;
}

message MColor4f {
required float R=1;
required float G=2;
required float B=3;
required float A=4;
}

message ResponseSection {
required uint32 MessageId=1;
required uint32 FailureCode=2;
}

message ProgramRegion {
required string ProgramName=1;
required uint32 ProgramMajorVersion=2;
required uint32 ProgramMinorVersion=3;
required uint32 ProgramBuildNumber=4;
required uint32 ProgramRevision=5;
required uint32 ProtocolSpecificationMajorVersion=6; 
required uint32 ProtocolSpecificationMinorVersion=7; 
required uint32 ProtocolBuildNumber=8;
required uint32 ProtocolRevision=9;
}

message IdentitySection {
required string ObjectId=1;
required string TypeId=2;
required string ParentId=3;
required string OwnerId=6;
required string ObjectName=7;
required bool Persistent=8;
required bool Observer=9;
}

message OrientationSection {
required MVector3f Location=1;
required MQuaternion4f Orientation=1;
}

message MotionSection {
required MVector3f Velocity=2;
required MQuaternion4f AngularVelocity=2;
}


message ForceSection {
required MVector3f Acceleration=1;
required MQuaternion4f AngularAcceleration=2;
}

message BodySection {
required float BoundingRadius=1;
required float Mass=2;
}

message ObjectSection {
optional uint32 ObjectIndex=1;
optional IdentitySection Identity=2;
optional OrientationSection Orientation=3;
optional MotionSection Motion=4;
optional ForceSection Force=5;
optional BodySection Body=6;
extensions 100 to 1000;
}

message InteractionSection {
required string InteractionName=1;
required string SourceParticipantId=2;
required string SourceObjectId=3;
required string TargetParticipantId=4;
required string TargetObjectId=5;
extensions 100 to 1000;
}

message BubbleSection {
required string BubbleId=1;
required string BubbleName=2;
required string BubbleAssetUrl=3;
required string OwnerId=4;
required string BubbleAddress=5;
required uint32 BubblePort=6;
required MVector3f BubbleCenter=7;
required float BubbleRange=8;
required float BubblePerceptionRange=9;
}

message JoinRequest {
required uint32 MessageId=1;
optional string BubbleId=2;
optional string BubbleName=3;
optional string LocationName=4;
required string ParticipantId=5;
optional string ParticipantSecret=6;
required string AvatarId=7;
required ProgramRegion ClientProgram=8;
}

message JoinResponse {
required uint32 MessageId=1;
required string BubbleId=2;
required string ParticipantId=3;
required string AvatarId=4;
required string BubbleName=5;
required string BubbleAssetUrl=6;
required float BubbleRange=7;
required float BubblePerceptionRange=8;
}

message LeaveRequest {
required uint32 MessageId=1;
}

message LeaveResponse {
required uint32 MessageId=1;
required ResponseSection Response=2;
}

message InjectRequest {
required uint32 MessageId=1;
optional ObjectSection Object=2;
}

message InjectResponse {
required uint32 MessageId=1;
required ResponseSection Response=2;
}

message EjectRequest {
required uint32 MessageId=1;
required string ObjectId=2;
}

message EjectResponse {
required uint32 MessageId=1;
required ResponseSection Response=2;
}

message InteractRequest {
required uint32 MessageId=1;
required InteractionSection Interaction=2;
}

message InteractResponse {
required uint32 MessageId=1;
required ResponseSection Response=2;
required InteractionSection Interaction=3;
}

message AttachRequest {
required uint32 MessageId=1;
required string TargetBubbleId=2;
required BubbleSection SourceBubble=3;
required ProgramRegion SourceProgram=4;
}

message AttachResponse {
required uint32 MessageId=1;
required ResponseSection Response=2;
required BubbleSection TargetBubble=3;
required ProgramRegion TargetProgram=4;
}

message DetachRequest {
required uint32 MessageId=1;
}

message DetachResponse {
required uint32 MessageId=1;
required ResponseSection Response=2;
}

message HandoverRequest {
required uint32 MessageId=1;
required string SourceBubbleId=2;
required string TargetBubbleId=3;
required ObjectSection Object=4;
}

message HandoverResponse {
required uint32 MessageId=1;
required ResponseSection Response=2;
}

enum ListType {
    Hosted = 0;
    Linked = 1;
    Connected = 2;
}

message ListBubblesRequest {
required uint32 MessageId=1;
required ListType listType=2;
}

message ListBubblesResponse {
required uint32 MessageId=1;
required ResponseSection Response=2;
repeated BubbleSection Bubble=3;
}

message PerceptionEvent {
required uint32 MessageId=1;
required ObjectSection Object=2;
}

message DisappearanceEvent {
required uint32 MessageId=1;
required uint32 ObjectIndex=2;
}

message MovementEvent {
required uint32 MessageId=1;
required uint32 ObjectIndex=2;
required MVector3f Location=3;
required MQuaternion4f Orientation=4;
}

message MovementEvent2 {
required uint32 ObjectIndex=2;
required float LocationX=3;
required float LocationY=4;
required float LocationZ=5;
required float OrientationX=6;
required float OrientationY=7;
required float OrientationZ=8;
required float OrientationW=9;
}

message ActionEvent {
required uint32 MessageId=1;
required string ActionName=2;
required string ObjectId=3;
required float EffectRadius=4;
extensions 100 to 1000;
}

message InteractionEvent {
required uint32 MessageId=1;
required string InteractionName=2;
required string SourceObjectId=3;
required string TargetObjectId=4;
required float EffectRadius=5;
extensions 100 to 1000;
}

message HandoverEvent {
required uint32 MessageId=1;
required string SourceBubbleId=2;
required string TargetBubbleId=3;
required ObjectSection Object=4;
}

message SynchronizationBeginEvent {
required uint32 MessageId=1;
required uint32 ObjectCount=2;
}

message SynchronizationEndEvent {
required uint32 MessageId=1;
}