Can length annotations for the output sizes of returned arrays be added?

For example the spec says here that the length of displayRefreshRates is displayRefreshRateCapacityInput, but this doesn't tell the whole story after the function is called! Is it possible to expand the spec with information about how many values in the array are valid (i.e. displayRefreshRateCountOutput) after the call returns?

      <command successcodes="XR_SUCCESS,XR_SESSION_LOSS_PENDING" errorcodes="XR_ERROR_INSTANCE_LOST,XR_ERROR_SESSION_LOST,XR_ERROR_RUNTIME_FAILURE,XR_ERROR_HANDLE_INVALID,XR_ERROR_SIZE_INSUFFICIENT,XR_ERROR_FUNCTION_UNSUPPORTED,XR_ERROR_VALIDATION_FAILURE">
        <proto><type>XrResult</type> <name>xrEnumerateDisplayRefreshRatesFB</name></proto>
        <param><type>XrSession</type> <name>session</name></param>
        <param optional="true"><type>uint32_t</type> <name>displayRefreshRateCapacityInput</name></param>
        <param><type>uint32_t</type>* <name>displayRefreshRateCountOutput</name></param>
        <param optional="true" len="displayRefreshRateCapacityInput"><type>float</type>* <name>displayRefreshRates</name></param>
      </command>

FWIW the Vulkan spec uses the same parameter for input and output so doesn't fall into this problem, although it's probably too late to change things now!

Start with the XML command definition for xrEnumerateDisplayRefreshRatesFB shown in the issue, focusing on displayRefreshRateCapacityInput, displayRefreshRateCountOutput, and displayRefreshRates. Review how the specification represents output-array validity, then determine whether the requested annotation can be expressed consistently. Done means the specification clearly communicates how many returned array values are valid, or documents why it cannot.