Hi Aaron,

I really appreciate your feedback. That helped fine-tune my implementation
of details/summary.

I now moved that code to the ox-blackfriday library when I have this in
org-blackfriday-special-block:

It's basically QOL code:

1. Wraps the "details" portion in "<p class="details"> .. </p>".
2. Accepts only ":open t" as a "true condition" to keep the details widget
open by default. Detecting that inserts just "open" in the "details"
element. So ":open nil" or ":open foo" would not result in inserting any
open attr at all.

The modified contents and attr-str in the below snippet are later used as:
(format "<%s%s>\n%s\n</%s>"
                block-type attr-str contents block-type)

         ((string= block-type "details")
          (setq contents
                (let* ((str1 (concat contents "\n</p>"))
                       (str2 (replace-regexp-in-string
                              "<summary>\\(?:.\\|\n\\)*</summary>"
                              "\\&\n<p class=\"details\">"
                              str1))
                       (has-summary (not (string= str1 str2))))
                  (unless has-summary
                    (setq str2 (concat "<p class=\"details\">" str1)))
                  str2))
          ;; Insert the "open" attribute only if user has ":open t" in
          ;; "#+attr_html".
          (when (org-string-nw-p attr-str)
            (when (string-match "\\(?1:open\\(?2:=\"\\(?3:t\\)\"\\)\\)"
attr-str)
              (if (match-string 3 attr-str) ;if attr-str contains `open="t"'
                  (setq attr-str (replace-match "" nil nil attr-str 2))
                (setq attr-str (replace-match "" nil nil attr-str 1))))))

-- 

Kaushal Modi