public Object eval(Object str, Object[] choices, boolean emptyOK) throws CMException
				{ // timeexpression
					if (!(str instanceof String))
						throw new CMException("Bad type: " + ((str == null) ? "null" : str.getClass().getName()));
					if (((String) str).trim().length() == 0)
					{
						if (emptyOK)
							return "";
						throw new CMException("You must enter an expression!");
					}
					if (!CMLib.time().isTickExpression((String) str))
						throw new CMException("Invalid time mathematical expression.  Use numbers,+,-,*,/,(), and ? only.  You may add ticks, minutes, hours, days, mudhours, muddays, mudweeks, mudmonths, mudyears.");
					return str;
				}