PlantUML sequence diagram

1. arrow

@startuml

header page1
title Test
footer page %page% of %lastpage%

== sycn call and return ==
A -> B : a()
A <-- B : response

== self message ==
A -> A : a()
A <- A : a()

== arrow styles ==

A ->x B
A -> B : sync call
A ->> B : async call
A -\ B : async call
A <-- B :return

== arrow color == 
A -[#red]> B : red
A <-[#0000FF]- B: blue

== auto number ==

autonumber
A -> B : 1
A <-- B : 2

autonumber 20
A --> B : 20


newpage

== now page 1 ==

A -[#red]> B: b()

@enduml

2. note, alt/group/loop/ref, activate

@startuml

header page2
title group
footer page %page% of %lastpage%

== note and alt/group/loop/ref example == 

alt if passed
    A -> B : success
    activate A

    A -> B : self message
    activate A #FFCCBB
    deactivate A


    deactivate A

    rnote left : ok

    ...
    ...

    ref over A: sequence diagram for success scenario
else
    A -> B : failure
    activate A

    hnote right : failure

    note over A, B #BBEEBB
        do fallback scenario A
    end note

    group fallback_a [fallback 1]
        loop until recovered
            A -> B : do fallback scenario
        end
    end

    deactivate A
end

note across
    note acroll all the components
end note

@enduml

@startuml

A -> B --++ : a()
return

A -> B ++ : a()
B -> B ++ : b()

@enduml

autoactivate

@startuml

header page2
title group
footer page %page% of %lastpage%

== autoactivate == 

autoactivate on

A -> B : a()
B -> B : b()
return res
return ok

A -> C ** : new
A -> C ++ : activate
return

A -> C !! : delete
...

@enduml