code: function parseAtomNames(atoms) {
    if (atoms === undefined || atoms === null || atoms === 'all') {
      return null;
    }
    if (atoms === 'backbone') {
      return { 'CA' : true, 'C' : true, 'O' : true, 'N' : true };
    }
    if (atoms.substr !== undefined) {
      var results = {};
      var atomNames = atoms.split(',');
      for (var i = 0; i < atomNames.length; ++i) {
        results[atomNames[i].trim()] = true;
      }
      return results;
    } else {
      var results = {};
      for (var i = 0; i < atoms.length; ++i) {
        results[atoms[i]] = true;
      }
      return results;
    }
  }
docs: Parses different representations of a list of atom names and returns a set (a dictionary actually with elements contained in the set set to true) that describes the list.  * undefined/null to null. This translates to match any atom * 'all' to null * 'backbone' to { 'N', 'CA', 'C', 'O' } * 'aname1, aname2' to { 'aname1', 'aname2' } * ['aname1', 'aname2']  to  { 'aname1', 'aname2' }