https://fossil-scm.org/home/vdiff?from=trunk&to=markdown-admonitions

Another experiment and proof of concept :)
If paragraph begins with special character set, add special styling or formatting.

They are:
:: FOLD :: enclose text in <details><summary> tags;
:: NOTE ::, :: TIP ::, :: IMPORTANT ::, :: CAUTION ::, :: WARNING :: add special styling.

Known implementations

• github-admonitions (discussion, blog post)
• asciidoc-admonitions
• asciidoc-collapsible
• markdown-it (codimd, VS Code)
• gitlab-collapsible

Known limitations

• no new lines, i.e. 1 or more blank line(s)
• no nested blocks?

Other thoughts

Not sure about names, and syntax, could be:

• different name, e.g. SPOILER, COLLAPSIBLE
• different syntax, e.g. [NOTE], %NOTE%, [!NOTE]
• lowercase vs. uppercase vs. case-insensitive
• allow any names (alpha-num) to style paragraphs, just add built-in classes for known keywords