Editorial: LocalTZA input specification

The `LocalTZA` implementation-defined algorithm must accept the full
range of `Number` and not define its input to be a *time value* because
the algorithm is specified to take an already offset local time that can
be outside of the time value range.

This cleans up the specification text to clearly distinguish UTC time
values versus local time `Number` inputs and uses the same subscript
notation for both UTC and local time to make the text more clear.

spec.html

@@ -27494,15 +27494,17 @@ <h1>Week Day</h1>
       <!-- es6num="20.3.1.7" -->
       <emu-clause id="sec-local-time-zone-adjustment">
         <h1>LocalTZA ( _t_, _isUTC_ )</h1>
-        <p>LocalTZA( _t_, _isUTC_ ) is an implementation-defined algorithm that must return a number representing milliseconds suitable for adding to a Time Value. The local political rules for standard time and daylight saving time in effect at _t_ should be used to determine the result in the way specified in the following three paragraphs.</p>
-        <p>When _isUTC_ is true, <dfn>LocalTZA( _t_, true )</dfn> should return the offset of the local time zone from UTC measured in milliseconds at time represented by time value _t_ (UTC). When the result is added to _t_ (UTC), it should yield the local time.</p>
-        <p>When _isUTC_ is false, <dfn>LocalTZA( _t_, false )</dfn> should return the offset of the local time zone from UTC measured in milliseconds at local time represented by time value <dfn><emu-eqn>_t_<sub>local</sub> = _t_</emu-eqn></dfn>. When the result is subtracted from the local time <emu-eqn>_t_<sub>local</sub></emu-eqn>, it should yield the corresponding UTC.</p>
-        <p>When <emu-eqn>_t_<sub>local</sub></emu-eqn> represents local time repeating multiple times at a negative time zone transition (e.g. when the daylight saving time ends or the time zone adjustment is decreased due to a time zone rule change) or skipped local time at a positive time zone transitions (e.g. when the daylight saving time starts or the time zone adjustment is increased due to a time zone rule change), <emu-eqn>_t_<sub>local</sub></emu-eqn> must be interpreted with the time zone adjustment before the transition.</p>
+        <p>LocalTZA( _t_, _isUTC_ ) is an implementation-defined algorithm that returns the local time zone adjustment, or offset, in milliseconds. The local political rules for standard time and daylight saving time in effect at _t_ should be used to determine the result in the way specified in this section.</p>
+        <p>When _isUTC_ is true, <emu-eqn>LocalTZA( _t_<sub>UTC</sub>, true )</emu-eqn> should return the offset of the local time zone from UTC measured in milliseconds at time represented by time value <emu-eqn>_t_<sub>UTC</sub></emu-eqn>. When the result is added to the time value <emu-eqn>_t_<sub>UTC</sub></emu-eqn>, it should yield the corresponding number <emu-eqn>_t_<sub>local</sub></emu-eqn>.</p>
+        <p>When _isUTC_ is false, <emu-eqn>LocalTZA( _t_<sub>local</sub>, false )</emu-eqn> should return the offset of the local time zone from UTC measured in milliseconds at local time represented by number <emu-eqn>_t_<sub>local</sub></emu-eqn>. When the result is subtracted from the local number <emu-eqn>_t_<sub>local</sub></emu-eqn>, it should yield the corresponding time value <emu-eqn>_t_<sub>UTC</sub></emu-eqn>.</p>
+        <p>Input _t_ is a Number that is nominally a time value but may be any Number value. This can occur when _isUTC_ is false and _t_<sub>local</sub> represents a time value that is already offset outside of the time value range at the range boundaries. The algorithm must not limit _t_<sub>local</sub> to the time value range, so that such inputs are supported.</p>
+        <p>When <emu-eqn>_t_<sub>local</sub></emu-eqn> represents local time repeating multiple times at a negative time zone transition (e.g. when the daylight saving time ends or the time zone offset is decreased due to a time zone rule change) or skipped local time at a positive time zone transitions (e.g. when the daylight saving time starts or the time zone offset is increased due to a time zone rule change), <emu-eqn>_t_<sub>local</sub></emu-eqn> must be interpreted using the time zone offset before the transition.</p>
         <p>If an implementation does not support a conversion described above or if political rules for time _t_ are not available within the implementation, the result must be 0.</p>
         <emu-note>
           <p>It is recommended that implementations use the time zone information of the IANA Time Zone Database <a href="https://www.iana.org/time-zones/">https://www.iana.org/time-zones/</a>.</p>
           <p>1:30 AM on November 5, 2017 in America/New_York is repeated twice (fall backward), but it must be interpreted as 1:30 AM UTC-04 instead of 1:30 AM UTC-05. LocalTZA(TimeClip(MakeDate(MakeDay(2017, 10, 5), MakeTime(1, 30, 0, 0))), false) is <emu-eqn>-4 &times; msPerHour</emu-eqn>.</p>
           <p>2:30 AM on March 12, 2017 in America/New_York does not exist, but it must be interpreted as 2:30 AM UTC-05 (equivalent to 3:30 AM UTC-04). LocalTZA(TimeClip(MakeDate(MakeDay(2017, 2, 12), MakeTime(2, 30, 0, 0))), false) is <emu-eqn>-5 &times; msPerHour</emu-eqn>.</p>
+          <p>Local time zone offset values may be positive *or* negative.</p>
         </emu-note>
       </emu-clause>
 
@@ -27514,19 +27516,20 @@ <h1>LocalTime ( _t_ )</h1>
           1. Return _t_ + LocalTZA(_t_, *true*).
         </emu-alg>
         <emu-note>
-          <p>Two different time values (_t_ (UTC)) are converted to the same local time <emu-eqn>t<sub>local</sub></emu-eqn> at a negative time zone transition when there are repeated times (e.g. the daylight saving time ends or the time zone adjustment is decreased.).</p>
+          <p>Two different input time values <emu-eqn>_t_<sub>UTC</sub></emu-eqn> are converted to the same local time <emu-eqn>t<sub>local</sub></emu-eqn> at a negative time zone transition when there are repeated times (e.g. the daylight saving time ends or the time zone adjustment is decreased.).</p>
+          <p><emu-eqn>LocalTime(UTC(_t_<sub>local</sub>))</emu-eqn> is not necessarily always equal to <emu-eqn>_t_<sub>local</sub></emu-eqn>. Correspondingly, <emu-eqn>UTC(LocalTime(_t_<sub>UTC</sub>))</emu-eqn> is not necessarily always equal to <emu-eqn>_t_<sub>UTC</sub></emu-eqn>.</p>
         </emu-note>
       </emu-clause>
 
       <!-- es6num="20.3.1.10" -->
       <emu-clause id="sec-utc-t" aoid="UTC">
         <h1>UTC ( _t_ )</h1>
-        <p>The abstract operation UTC with argument _t_ converts _t_ from local time to UTC. It performs the following steps:</p>
+        <p>The abstract operation UTC with argument _t_ converts _t_ from local time to UTC by performing the following steps:</p>
         <emu-alg>
           1. Return _t_ - LocalTZA(_t_, *false*).
         </emu-alg>
         <emu-note>
-          <p><emu-eqn>UTC(LocalTime(_t_))</emu-eqn> is not necessarily always equal to _t_. <emu-eqn>LocalTime(UTC(_t_<sub>local</sub>))</emu-eqn> is not necessarily always equal to <emu-eqn>_t_<sub>local</sub></emu-eqn>, either.</p>
+          <p><emu-eqn>UTC(LocalTime(_t_<sub>UTC</sub>))</emu-eqn> is not necessarily always equal to <emu-eqn>_t_<sub>UTC</sub></emu-eqn>. Correspondingly, <emu-eqn>LocalTime(UTC(_t_<sub>local</sub>))</emu-eqn> is not necessarily always equal to <emu-eqn>_t_<sub>local</sub></emu-eqn>.</p>
         </emu-note>
       </emu-clause>