lots of example a.m. p.m. periods

periods.js

// this isn't all the possible valid periods, but it's a good batch
var periods = []
  , seed = ['pm', 'p', 'p.m.', 'pm.', 'p.m'];

for (var i=0; i<seed.length; i++) {
  var s = seed[i];
  periods.push(s);
  periods.push(s.toUpperCase());
  periods.push(s.replace('m', 'M'));
  periods.push(s.replace('p', 'P'));
  periods.push(s.replace('p', 'a'));
  periods.push(s.toUpperCase());
  periods.push(s.toUpperCase().replace('M', 'm'));
  periods.push(s.replace('a', 'A'));
}