List of overridden environment variables for subprocesses to inherit.
Each element should be a string of the form ENVVARNAME=VALUE.
Entries in this list take precedence to those in the frame-local
environments. Therefore, let-binding `process-environment' is an easy
way to temporarily change the value of an environment variable,
irrespective of where it comes from. To use `process-environment' to
remove an environment variable, include only its name in the list,
without "=VALUE".
This variable is set to nil when Emacs starts.
If multiple entries define the same variable, the first one always
takes precedence.
Non-ASCII characters are encoded according to the initial value of
`locale-coding-system', i.e. the elements must normally be decoded for
use.
See `setenv' and `getenv'.