How to create sequence diagrams?
Add a sequence diagram from the palette sequence_palette2. The sequence diagram is powered by a simple grammar. In the following is an explaination of the diagrams grammar using the example from the palette:

//UML2 style titles are optional.
title:sequence diagram
//the participating objects are separated using the pipe symbol "|". Their names may be underlined using underscores.
_alpha:A_|_beta:B_|_gamma:G_
//The following line describes a (synchonuous) message originating from the first object sent to the second object, while both objects are active.
1->>2:1,2
//This message is asynchronous being sent from the second object to the first object. The messages is named.
2-/>1:async Msg.
//A message from the third object to the first object; both objects are active.
3->>>1:1,3
//A named asynchronous return message in UML2 style (using a stick arrow head).
1.>3:1,3:async return Msg
//This is a self call of the first object.
1->1:1:self
//Interaction frames may be used to show optional or conditional blocks within sequence diagrams.
iframe{:interaction frame
2->3:2,3:async Msg.
iframe}