\brief Retrieve the annotation associated with the given completion string.
\param completion_string the completion string to query.
\param annotation_number the 0-based index of the annotation of the completion string.
\returns annotation string associated with the completion at index \c annotation_number, or a NULL string if that annotation is not available.
See Implementation
\brief Retrieve the annotation associated with the given completion string.
\param completion_string the completion string to query.
\param annotation_number the 0-based index of the annotation of the completion string.
\returns annotation string associated with the completion at index \c annotation_number, or a NULL string if that annotation is not available.