Editorial: Clarify note about M00L

Clarify that this month code doesn't exist in any currently supported
calendars, with "theoretically".

Author: ptomato

spec/calendar.html

@@ -101,7 +101,7 @@ <h1>Calendar Date Records</h1>
             <td>
               The month code of the date's month. The month code for a month that is not a leap month and whose 1-based ordinal position in a common year of the calendar (i.e., a year that is not a leap year) is _n_ should be the string-concatenation of *"M"* and ToZeroPaddedDecimalString(_n_, 2), and the month code for a month that is a leap month inserted after a month whose 1-based ordinal position in a common year of the calendar is _p_ should be the string-concatenation of *"M"*, ToZeroPaddedDecimalString(_p_, 2), and *"L"*.
               <emu-note>
-                For example, in the Hebrew calendar, the month code of Adar (and Adar II, in leap years) is *"M06"* and the month code of Adar I (the leap month inserted before Adar II) is *"M05L"*. In a calendar with a leap month at the start of some years, the month code of that month would be *"M00L"*.
+                For example, in the Hebrew calendar, the month code of Adar (and Adar II, in leap years) is *"M06"* and the month code of Adar I (the leap month inserted before Adar II) is *"M05L"*. Theoretically, in a calendar with a leap month at the start of some years, the month code of that month would be *"M00L"*.
               </emu-note>
             </td>
           </tr>