Hello,

I have this test case; export it by doing C-c C-e C-s m M (assuming ox-md
is required.. I think it is required by default).

=====
* Escaping hashes and exclamations correctly in body
:PROPERTIES:
:EXPORT_FILE_NAME: escaping-hashes-and-exclamations-in-body
:END:
I intend to show these # characters verbatim; they should not render
as Markdown headings. They also shouldn't show up with a leading =\=
in the final rendered output.

# This is an Org comment

#This is not an Org comment. It has a hash char at beginning of a
paragraph which must be escaped just once i.e. show up as =\#= in
Markdown.

blah # This isn't an Org comment either

This * will be escaped just once i.e. show up as =\*= in Markdown.

This _ will be escaped just once i.e. show up as =\_= in Markdown.

This \ will be escaped just once i.e. show up as =\\= in Markdown.

Hash char at beginning of a continued line
#like this must be escaped just once i.e. show up as =\#= in Markdown.

![this exclamation must be escaped just once i.e. show up as =\!= in
Markdown]

This ! does not need to be escaped as there is no ambiguity.
=====

Here's the relevant excerpt of the export that is erroneous:

=====
Hash char at beginning of a continued line
\\#like this must be escaped just once i.e. show up as `\#` in Markdown.

\\![this exclamation must be escaped just once i.e. show up as `\!` in
Markdown]
=====

Note that the # and ![ are double-escaped. So any markdown->HTML renderer
will print that "\" as it is.

Digging through ox-md.el, I found that the order of
replace-regexp-in-string was incorrect in org-md-plain-text.

Here's the diff:

=====
diff --git a/lisp/ox-md.el b/lisp/ox-md.el
index 12188387355..927a73b780c 100644
--- a/lisp/ox-md.el
+++ b/lisp/ox-md.el
@@ -500,14 +500,15 @@ TEXT is the string to transcode.  INFO is a plist
holding
 contextual information."
   (when (plist-get info :with-smart-quotes)
     (setq text (org-export-activate-smart-quotes text :html info)))
+  ;; The below series of replacements in `text' is order sensitive.
+  ;; Protect `, *, _, and \
+  (setq text (replace-regexp-in-string "[`*_\\]" "\\\\\\&" text))
   ;; Protect ambiguous #.  This will protect # at the beginning of
   ;; a line, but not at the beginning of a paragraph.  See
   ;; `org-md-paragraph'.
   (setq text (replace-regexp-in-string "\n#" "\n\\\\#" text))
   ;; Protect ambiguous !
   (setq text (replace-regexp-in-string "\\(!\\)\\[" "\\\\!" text nil nil
1))
-  ;; Protect `, *, _ and \
-  (setq text (replace-regexp-in-string "[`*_\\]" "\\\\\\&" text))
   ;; Handle special strings, if required.
   (when (plist-get info :with-special-strings)
     (setq text (org-html-convert-special-strings text)))
=====

After applying this patch, the same portion exported doesn't have
double-escaping before # and ![.

If this looks good, I can commit this to maint.

-- 

Kaushal Modi