You can use (*) for the starting point and ending point of the activity diagram. In some occasion, you may want to use (*top) to force the starting point to be at the top of the diagram. Use --> for arrows.
When you declare activities, you can span on several lines the description text. You can also add \n in the description. You can also give a short code to the activity with the as keyword. This code can be used latter in the diagram description.
(*) -left-> "this <size:20>action</size>
is <b>very</b> <color:red>long2</color>
and defined on several lines
that contains many <i>text</i>" as A1
-up-> "Another action\n on several lines"
A1 --> "Short action <img:sourceforge.jpg>"
You can add notes on a activity using the commands note left, note right, note top or note bottom, just after the description of the activity you want to note. If you want to put a note on the starting point, define the note at the very beginning of the diagram description. You can also have a note on several lines, using the endnote keywords.
(*) --> "Some action"
note right: This action has to be defined
"Some action" --> (*)
This note is on
You can define a partition using the partition keyword, and optionally declare a background color for your partition (Using a html color code or name) When you declare activities, they are automatically put in the last used partition. You can close the partition definition using a closing bracket }.