ZenUML is an alternative sequence diagram notation with a more code-like syntax than the standard Mermaid sequence diagram. Rather than listing each message on a separate line, ZenUML uses a nested structure that mirrors how actions and responses group together naturally.

Both ZenUML and the standard sequence diagram (sequenceDiagram) produce similar output; ZenUML may feel more intuitive to authors who prefer an indented, block-based writing style.

zenuml
    @Actor Customer
    @Boundary Website
    @Control SupportAgent

    Customer -> Website.openChat("Start chat") {
        Website -> SupportAgent.notify("Customer waiting")
        SupportAgent -> Customer.greet("Hello! How can I help?")
    }
    Customer -> SupportAgent.describe("I can't find my order")
    SupportAgent -> Customer.sendLink("Here is your order tracking link")
    Customer -> SupportAgent.confirm("Found it, thank you!")

ZenUML diagrams begin with participant declarations (using @Actor, @Boundary, @Control, and similar tags) followed by message chains. Nested braces group related responses under their triggering action.

```mermaid
zenuml
    @Actor Customer
    @Boundary Website
    @Control SupportAgent

    Customer -> Website.openChat("Start chat") {
        Website -> SupportAgent.notify("Customer waiting")
        SupportAgent -> Customer.greet("Hello! How can I help?")
    }
    Customer -> SupportAgent.describe("I can't find my order")
    SupportAgent -> Customer.sendLink("Here is your order tracking link")
    Customer -> SupportAgent.confirm("Found it, thank you!")
```

For more ZenUML syntax see the ZenUML documentation at mermaid.js.org