The fact that it's sometimes optional doesn't mean it's always optional. 
>c:\foo bar\test.pl
'c:\foo' is not recognized as an internal or external command,
operable program or batch file.

>"c:\foo bar\test.pl"
Hello World

[download]

The same applies for the registry where command lines are expected such as in file associations.

In reply to Re^3: Using regex to separate parameters by ikegami
in thread Using regex to separate parameters by resistance

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