message: Update API document on Span functions to clarify initialization
diff: @@ -100,11 +100,12 @@ public:
  * Put signature that provides access to the internal engine buffer for a
  * pre-allocated variable including a fill value. Returns a fixed size Span
  * (based on C++20 std::span) so applications can populate data value after
  - * this Put. Requires a call to PerformPuts, EndStep, or Close to extract
  - * the Min/Max bounds.
  + * this Put and before PerformPuts/EndStep. Requires a call to PerformPuts,
  + * EndStep, or Close to extract the Min/Max bounds.
  * @param variable input variable
  * @param initialize bool flag indicating if allocated memory should be
  - * initialized with the provided value
  + * initialized with the provided value. Some engines (BP3/BP4) may
  + * initialize the allocated memory anyway to zero if this flag is false.
  * @param value provide an initial fill value
  * @return span to variable data in engine internal buffer
  */
  @@ -114,8 +115,9 @@ public:
  /**
  * Put signature that provides access to an internal engine buffer (decided
  - * by the engine) for a pre-allocated variable with the default fill value
  - * T().
  + * by the engine) for a pre-allocated variable. Allocated buffer may or may
  + * not be initialized to zero by the engine (e.g. BP3/BP4 does, BP5 does
  + * not).
  * @param variable input variable
  * @return span to variable data in engine internal buffer
  */
  