>> I've incorporated the following suggestions:
>>
>> - Order of precedence:
>>   + #+attr_org overrides #+attr_html and #+attr_latex
>>   + `:center t' overrides `:align ...'
>
> Why only html and latex? I think that it will be more consistent to
> follow what we do in `org-display-inline-image--width' - any #+attr_*
> attribute. And apart from html/latex, we have
> beamer/hugo/koma-letter/what not is implemented or will be implemented
> deriving from html/latex backend or with support of :center attribute.

Changed implementation to support any #+attr_.* keyword.

>> - Add a checker for `:align nil' to org-lint.  `:align nil' is not
>>   supported.
>
> I meant :align <anything> being not supported in #+attr_org. Not just nil.

org-lint now complains if anything other than `:align left|center|right'
or `:center t' are specified in #+attr_org.

>> +  #+vindex: org-image-align
>> +  Org mode can left-align, center or right-align the display of inline
>> +  images.  This setting is controlled (globally) by ~org-image-align~.
>> +  Only standalone links, /i.e/ links with no surrounding text in their
>
> Maybe "standalone images"?
> Also, please avoid i.e - this is a general Emacs documentation guideline
> to avoid specialized language like i.e., e.g., and iff.

Changed text, removed specialized language.

>> +  paragraphs (except whitespace) are affected.  Its value can be the
>> +  following:
>> +  - (default) nil, insert the image where the link appears in the
>> +    buffer.
>
> Why not simply setting the default to 'left and not having nil at all?

The original idea was that `left' and `nil' do the same thing, so it
should be fine to leave it at `nil'.  I changed the user option to
default to `left', and `nil' has been removed as an available option.
(It is still not an error to set it to `nil'.)

>> +  - The symbol ~left~, which is the same as nil.
>> +  - The symbol ~center~, which will preview standalone links centered
>> +    in the Emacs window.
>> +  - The symbol ~right~, which will preview standalone links
>> +    right-aligned in the Emacs window.
>
> "standalone" links is redundant here - you already mentioned that  

Fixed.

>> +  Inline image alignment can be specified for each link using the
>> +  =#+ATTR.*= keyword if it matches an alignment specification like:
>> +  #+begin_example
>> +  ,#+ATTR_HTML: :align center
>> +  #+end_example
>> +  Supported values for =:align= are =left=, =center= and =right=.
>
> I think that we do not need to specify the supported values here - they
> are the same as for `org-image-align' just above.

Removed.

>> +  Inline image display can also be centered using =:center=, as in
>
> I'd explain that inline image adjustment is also taken from :center
> attribute supported by some export backends (like HTML, LaTeX, and
> Beamer), when #+attr_org is not set.

Tweaked the description of :center.

>> +  #+begin_example
>> +  ,#+ATTR_HTML: :center t
>> +  #+end_example
>> +  Org will use the alignment specification from any =#+ATTR.*=
>> +  keyword, such as =#+ATTR_HTML= or =#+ATTR_LATEX=, but =#+ATTR_ORG=
>> +  (if present) will override the others.  For instance, this link
>> +  #+begin_example
>> +  ,#+ATTR_HTML: :align right
>> +  ,#+ATTR_ORG: :align center
>> +  [[/path/to/image/file.png]]
>> +  #+end_example
>> +  will be displayed centered.
>
> ... "but exported right-aligned to HTML"

Added.

>> +(defun org-lint-invalid-image-alignment (ast)
>> +  (org-element-map ast 'paragraph
>> +    (lambda (p)
>> +      (let ((bad-align-re ":align[[:space:]]+nil")
>> +            (keyword-string (mapconcat
>> +                             (lambda (attr)
>> +                               (or (car-safe (org-element-property attr p)) ""))
>> +                             '(:attr_org :attr_latex :attr_html) " ")))
>
> :align nil is perfectly valid for HTML.
> I thought to warn only about using anything but :align left/right/center
> in #+attr_org. And about :center <anything> in #+attr_org.

Yes, only the value of #+attr_org is checked now.

Patch v2 attached.

Karthik