| Allowed Value | Details | 
|---|---|
| backbone turn | |
| bent/kinked double helix | |
| intercalated base | |
| intramolecular base triplet | |
| pseudoknot | |
| purine platform | |
| ribose zipper | 
| Allowed Value | Details | 
|---|---|
| backbone turn | |
| bent/kinked double helix | |
| intercalated base | |
| intramolecular base triplet | |
| pseudoknot | |
| purine platform | |
| ribose zipper |