docs: function compile(parsed) {
      var a = parsed[0],
          b = parsed[1] - 1;
  
      //when b <= 0, a*n won't be possible for any matches when a < 0
      //besides, the specification says that no element is matched when a and b are 0
      if (b < 0 && a <= 0) return falseFunc;
  
      //when a is in the range -1..1, it matches any element (so only b is checked)
      if (a === -1)
          return function(pos) {
              return pos <= b;
          };
      if (a === 0)
          return function(pos) {
              return pos === b;
          };
      //when b <= 0 and a === 1, they match any element
      if (a === 1)
          return b < 0
              ? trueFunc
              : function(pos) {
                    return pos >= b;
                };
  
      //when a > 0, modulo can be used to check if there is a match
      var bMod = b % a;
      if (bMod < 0) bMod += a;
  
      if (a > 1) {
          return function(pos) {
              return pos >= b && pos % a === bMod;
          };
      }
  
      a *= -1; //make `a` positive
  
      return function(pos) {
          return pos <= b && pos % a === bMod;
      };
  }