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This should be handled in _winapi.CreateProcess(). An environment block is technically required to be sorted. (Ages ago this was a MUST requirement for getting and setting variables to work correctly, since the implementation depended on the sort order, but I think nowadays it's a SHOULD requirement.) For example, see the documentation of CreateProcessW() [1]:
 If an application provides an environment block, ... explicitly create
 these environment variable strings, sort them alphabetically (because
 the system uses a sorted environment)
"Changing Environment Variables" is more specific [2]:
 All strings in the environment block must be sorted alphabetically by name.
 The sort is case-insensitive, Unicode order, without regard to locale.
CompareStringOrdinal() [3] implements a case-insensitive ordinal comparison. When a key compares as equal, either keep the current one in the sorted list, or replace it with the new key.
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[1] https://docs.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-createprocessw
[2] https://docs.microsoft.com/en-us/windows/win32/procthread/changing-environment-variables
[3] https://docs.microsoft.com/en-us/windows/win32/api/stringapiset/nf-stringapiset-comparestringordinal