Can not find large string data using Reportable REST API

Hello!
This page describes Reportable REST API which I can use building custom reports:

https://jazz.net/wiki/bin/view/Main/ReportsRESTAPI

For "workItem (type: com.ibm.team.workitem.WorkItem)" section (building an RTC report), I can find "description" element which is multiline string.



But when I try use this element anywhere, I can not find it.



The sample above is from BIRT report. But I didn't find description element in RRDI live model as well!
As I understand, I can not find here not only description of workitem but any custom large string data too!

Can somebody point what is wrong in my actions? May be there's a specific way to extract this kind of data?

Thank you very much for any help!