How to decrypt a message while preserving the signature?

[Tony Lane]

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On 11/3/19 4:15 AM, Peter Lebbing wrote:
> Werner recently mentioned an undocumented command for this.[1]
> 
> On 27/08/2019 11:30, Werner Koch via Gnupg-users wrote: 
>> You can extra the signature from the encrypted+signed data:
>>
>>   gpg --unwrap -d -o SIG <ENC+SIG
>>
>> and then run
>>
>>   gpgv -o SIGNEDFILE SIG && echo verified!
>>

The '--unwrap' option alone seems to work for me. Thanks for sharing this.

> --unwrap is not documented and has the minor problem that it also keeps the
compression layer

Why is keeping the compression layer a problem? Also what other undocumented options are out there?
Can they be documented somewhere?
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