Robert Nikander <robert.nikander@icloud.com> writes:

> Hitting TAB on the BEGIN line does nothing. But if I add a blank line before it, then hitting TAB hides and shows the block. Is that a bug? Or am I doing it wrong? Seems like it should work without the blank line.
>
> * Test
> Some text
>
> #+BEGIN 
> Hide this
> #+END
>
> M-x org-version => 9.5.1.

This last case is actually a bug. As Tomas pointed, Org blocks have
slightly different syntax: either #+begin_something or #+begin:
typeofblock. The fact that you can fold the #+BEGIN..#+END in your
second case should not happen.

The fix is attached.

Nicolas,
Let me know if I miss something about special block parsing.

Best,
Ihor