bug#25578: [PATCH] Prompt default extension in dired-mark-extension

[Juri Linkov]

>>> I want 'M-x dired-mark-extension' (from dired-x) in Dired to use the
>>> extension of the file at point as default extension, when it is
>>> possible. Because, in this way, I usually no longer need to type the
>>> extension manually, which saves some time for me–someone can't type
>>> English words quickly and accurately.
>>
>> Thanks, I think your patch is a useful addition.
> I agree, it's a good default value.
>>
>> Also I'm using a similar feature for another Dired command
>> ‘dired-mark-files-regexp’ that could provide similar defaults
>> based on the current file and its extension:
> That's also fine.

Thanks for your support.  Done and done.