Clarify that keyframes are not replicated in nested attachments.

PiperOrigin-RevId: 663683684
Change-Id: Id180b3a6afad6809d8189a7a525c474bd3a91fc1

doc/APIreference/APItypes.rst

@@ -1393,6 +1393,8 @@ Alternative orientation specifiers.
 
 .. _ArrayHandles:
 
+.. _mjBuffer:
+
 .. _mjString:
 
 .. _mjStringVec:
@@ -1417,6 +1419,7 @@ C handles for C++ strings and vector types. When using from C, use the provided
 
    #ifdef __cplusplus
      // C++: defined to be compatible with corresponding std types
+     using mjBuffer      = std::vector<std::byte>;
      using mjString      = std::string;
      using mjStringVec   = std::vector<std::string>;
      using mjIntVec      = std::vector<int>;
@@ -1426,6 +1429,7 @@ C handles for C++ strings and vector types. When using from C, use the provided
      using mjDoubleVec   = std::vector<double>;
    #else
      // C: opaque types
+     typedef void mjBuffer;
      typedef void mjString;
      typedef void mjStringVec;
      typedef void mjIntVec;