Predefined sets consist of 'all', 'none', 'selected', the element names, and a number of protein .PDB specific sets.

'all' and 'none' should be self-explanatory. 'selected' allows you to use the currently selected set of atoms in a subsequent atom expression.

Element names can be used instead of 'elemno=#'. Both singular and plural forms of the element names may be used. The following are all equivalent: 'select hydrogen', 'select hydrogens', 'select elemno=1', 'select elemno==1'

When working with protein molecules in .PDB files you can use a number of predefined sets to select the atoms in amino acids or selected groups of amino acids.

All three letter amino abbreviations work. There are also single letter abbreviations which work. All are compatible with RasMol. ala(a), arg(r), asn(n), asp(d), cys(c), glu(e), gln(q), gly(g), his(h), ile(i), leu(l), lys(k), met(m), phe(f), pro(p), ser(s), thr(t), trp(w), tyr(y), val(v)

The following sets are defined as in RasMol: at, acidic, acyclic, aliphatic, alpha, amino, aromatic, backbone, basic, bonded, buried, cg, charged, cyclic, cystine, helix, hetero, hydrogen, hydrophobic, ions, large, ligand, medium, neutral, nucleic, polar, protein, purine, pyrimidine, sheet, sidechain, small, solvent, surface, turn, water.