Added recipe for parsing daylight transition times

Examples-and-Recipes.md

@@ -27,6 +27,7 @@ This page contains examples and recipes contributed by community members. Feel f
 - [How to convert to/from QDate](#QDate)
 - [How to convert to/from Windows' FILETIME](#FILETIME)
 - [Print out a compact calendar for the year](#calendar)
+- [Parsing unambiguous date time inside daylight transition](#parse_daylight_transition)
 
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@@ -1563,6 +1564,49 @@ which outputs:
      26 27 28 29 30          24 25 26 27 28 29 30    28 29 30                26 27 28 29 30 31   
                              31                                                                  
 
+<a name="parse_daylight_transition"></a>
+### Parsing unambiguous date time inside daylight transition
+(by [Tai Meng](https://github.com/ta1meng))
+
+We needed the ability to (de)serialize date time values. We investigated how we could parse an input string that looks like this:
+
+    1) 1999-10-31 01:30:00 US/Pacific PST
+
+After consulting [Howard](https://github.com/HowardHinnant), we learned that the input string should instead look like this:
+
+    2) 1999-10-31 01:30:00 -08:00 US/Pacific
+
+and then the solution is simple. To convert PST to -08:00 is in general non-trivial and often requires user input, because abbreviations often match multiple timezones. This recipe assumes that users of this recipe will have a way to re-format strings of form 1) into strings of form 2).
+
+Once we have a string of form 2), give this sample code a try (thank you [Aaron](https://github.com/ahn6) who provided the draft):
+
+      #include <iostream>
+      #include <sstream>
+      #include <string>
+      #include "tz.h"
+
+      void main()
+      {
+         using namespace std;
+         using namespace date;
+
+         istringstream inputStream{ "1999-10-31 01:30:00 -08:00 US/Pacific" };
+   
+         // Using local_seconds would resolve in ambiguous date exception
+         sys_seconds tp;
+         string tz_name;
+         parse(inputStream, "%F %T %Ez %Z", tp, tz_name);
+
+         // bool operator tells us whether stream was successfully parsed
+         assert(bool(inputStream));
+
+         auto zt = make_zoned(tz_name, tp);
+
+         // This will output America/Los_Angeles, because US/Pacific is an alias of it.
+         cout << format("%F %T %Ez", zt) << ' ' << zt.get_time_zone()->name() << '\n';
+      }
+
+
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