.. _ALT_A:

``ALT_A``
=========

Some PDB geometries have two or more possible positions for some atoms
(positional disorder). These are indicated by the letters 'A', 'B',
etc., before the three letter abbreviation for the residue. Only one
option for a set of atoms can be selected. To select all atoms of type
'A,' use ``ALT_A=A``; to select all those of type 'B,' use ``ALT_A=B``,
etc.

See also: ```PDB`` <pdb.html>`__, ```CHAINS`` <chains.html>`__