Unmentioned in all the previous looks at features is Microsoft Dynamics GP 2013 R2 updates to Report Writer Functions David Musgrave has coverage.
Microsoft Dynamics GP 2013 R2 updates to Report Writer Functions – Developing for Dynamics GP
Reporting & BIGP 2013
Archived post from 2014. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.