> On a casual inspection, it appears that ob-plantuml hardcodes the
> plantuml keywords @startuml/@enduml around the source block.

On closer inspection, I see that Org Mode 9.2.6 supports alternate
@start/@end pairs in plantuml. Rather than using a keyword on
#+BEGIN_SRC, it simply checks for @start… at the beginning of the
body.

That’s good enough, I think.

                                        Be seeing you,
                                          norm

-- 
Norman Walsh <ndw@nwalsh.com> | Four things come not back: the spoken
http://nwalsh.com/            | word, the sped arrow, time past, the
                              | neglected opportunity.--Omar Ibnal-Halif