| Allowed Value | Details | 
|---|---|
| T | special-position constraints on atomic displacement parameters | 
| TU | both constraints applied | 
| U | Uiso or Uij restraint (rigid bond) | 
| Allowed Value | Details | 
|---|---|
| T | special-position constraints on atomic displacement parameters | 
| TU | both constraints applied | 
| U | Uiso or Uij restraint (rigid bond) |