Make CalendarDateWeekOfYear return undefined

...for all calendars without well-defined week calendar system

spec/calendar.html

@@ -616,6 +616,7 @@ <h1>
           1. Set _calendar_ to ! CreateTemporalCalendar(_calendar_).
           1. Return ? Call(%Temporal.Calendar.prototype.weekOfYear%, _calendar_, « _dateLike_ »).
         1. Let _result_ be ? Invoke(_calendar_, *"weekOfYear"*, « _dateLike_ »).
+        1. If _result_ is *undefined*, return *undefined*.
         1. If Type(_result_) is not Number, throw a *TypeError* exception.
         1. If IsIntegralNumber(_result_) is *false*, throw a *RangeError* exception.
         1. If _result_ &lt; *1*<sub>𝔽</sub>, throw a *RangeError* exception.
@@ -639,6 +640,7 @@ <h1>
           1. Set _calendar_ to ! CreateTemporalCalendar(_calendar_).
           1. Return ? Call(%Temporal.Calendar.prototype.yearOfWeek%, _calendar_, « _dateLike_ »).
         1. Let _result_ be ? Invoke(_calendar_, *"yearOfWeek"*, « _dateLike_ »).
+        1. If _result_ is *undefined*, return *undefined*.
         1. If Type(_result_) is not Number, throw a *TypeError* exception.
         1. If IsIntegralNumber(_result_) is *false*, throw a *RangeError* exception.
         1. Return ℝ(_result_).

spec/intl.html

@@ -2023,6 +2023,15 @@ <h1>
             Usually the [[Year]] field will contain the same value given by CalendarDateYear, but may contain the previous or next year if the week number in the [[Week]] field overlaps two different years.
             See also ToISOWeekOfYear.
           </p>
+          <p>
+            It returns *undefined* in [[Week]] and [[Year]] field for calendars that do not have a well-defined week calendar system.
+          </p>
+          <emu-note type="editor">
+            <p>
+              More details about this function will be specified in
+              <a href="https://tc39.es/proposal-intl-era-monthcode/">the Intl era and monthCode proposal</a>.
+            </p>
+          </emu-note>
         </emu-clause>
 
         <emu-clause id="sec-temporal-calendardatedaysinweek" type="abstract operation">

spec/mainadditions.html

@@ -52,12 +52,12 @@ <h1>The Year-Week Record Specification Type</h1>
           <tbody>
             <tr>
               <td>[[Week]]</td>
-              <td>a positive integer</td>
+              <td>a positive integer or *undefined*</td>
               <td>The calendar week of year.</td>
             </tr>
             <tr>
               <td>[[Year]]</td>
-              <td>an integer</td>
+              <td>an integer or *undefined*</td>
               <td>The week calendar year.</td>
             </tr>
           </tbody>