https://mermaid.js.org/syntax/sequenceDiagram.html
https://mermaid.js.org/syntax/zenuml.html

https://kroki.io/
https://github.com/yuzutech/kroki
https://docs.kroki.io/kroki/setup/use-docker-or-podman/

https://typora.io/
https://github.com/typora
https://support.typora.io/
https://support.typora.io/Draw-Diagrams-With-Markdown/#sequence-diagrams
    –sequence-theme: hand

https://bramp.github.io/js-sequence-diagrams/

seqdiag {
  browser  -> webserver [label = "1. GET /seqdiag/svg/base64"];
  webserver  -> processor [label = "2. Convert text to image"];
  webserver <-- processor;
  browser <-- webserver;
}