Ramachandran plots of protein phi,psi backbone dihedral angles, for the six distinct amino-acid categories used in model validation at the worldwide Protein Data Bank since 2013. Data from about 1.5 million quality-filtered residues; contours from MolProbity. Inner contour encloses the "favored" region that includes 98% of the high-quality reference data; outer dark contour divides the "outlier" region from the "allowed" region.