[வியாழன் ஜனவரி 12, 2023] Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" wrote:

>> --- a/lisp/doc-view.el
>> +++ b/lisp/doc-view.el
>> @@ -921,7 +921,7 @@ doc-view-shrink-factor
>>  (defun doc-view-enlarge (factor)
>>    "Enlarge the document by FACTOR."
>>    (interactive (list doc-view-shrink-factor))
>> -  (if doc-view-scale-internally
>> +  (if (or doc-view-scale-internally doc-view-mupdf-use-svg)
>>        (let ((new (ceiling (* factor doc-view-image-width))))
>>          (unless (equal new doc-view-image-width)
>>            (setq-local doc-view-image-width new)
>> @@ -941,7 +941,7 @@ doc-view-shrink
>>  (defun doc-view-scale-reset ()
>>    "Reset the document size/zoom level to the initial one."
>>    (interactive)
>> -  (if doc-view-scale-internally
>> +  (if (or doc-view-scale-internally doc-view-mupdf-use-svg)
>>        (progn
>>  	(kill-local-variable 'doc-view-image-width)
>>  	(doc-view-insert-image
>
> Hmm.... `doc-view-mupdf-use-svg` means "use SVG when the backend
> is mupdf" but we don't know here whether the backend is mupdf, so this
> will misfire when using something else than mupdf, no?

Ah yes, of course.  Somehow, I managed to completely forget about the
other file formats supported by doc-view like djvu (since I only use
file formats that use mupdf in the end).  How about the below revised
patch?