The type of chiral problem that the label_atom_id has. One of:
(A) "mainchain": The N label_atom_id of an amino acid residue is expected to be in the same plane as the Calpha,
C, and O atoms of the previous residue. If the improper torsion angle of these atoms is more than 10
degrees, this is flagged as a planarity deviation. From mmcif item "_pdbx_validate_main_chain_plane".
(B) "peptide": A deviation is flagged if the omega torsion angle of a peptide group differs by more than 30
degrees from the values expected for a proper cis or trans conformation (0 degrees and 180 degrees,
respectively). For mmcif item: "_pdbx_validate_peptide_omega".
(C) "sidechain": Certain groups of atoms in protein sidechains and nucleotide bases are expected to be in
the same plane. An atom's deviation from planarity is calculated by fitting a plane through these atoms
and then calculating distance of individual label_atom_id from the plane. Expected value of such distances have
been pre-calculated from data analysis (wwPDB, 2012). If an label_atom_id is modelled to be more than six times
farther than the pre-calculated value, the residue is flagged to have a sidechain planarity deviation.
From mmcif item "_pdbx_validate_planes".