The following calls can be used to define a sequence diagram.

object(name,label);
  Defines an object with the given name, labeled on the diagram as specified.
placeholder_object(name)
  Defines a place where the named object will later be created. Can also be written as `pobject`.
actor(name,label);
  Defines an actor with the given name, labeled on the diagram as specified. Actors are typically used instead of objects to indicate operations initiated by human actions.
complete(name);
  Completes the lifeline of a given object (or actor) by drawing its lifeline to the bottom of the diagram.
message(from_object,to_object,label)
  Draws a message between two objects, with the given label. Self messages (where an objects sends a message to itself) are supported.
return_message(from_object,to_object,label)
  Draws a return message between two objects, with the given label. Can also be written as `rmessage`.
create_message(from_object,to_object,object_label);
  Has from_object create the to_object, labeled with object_label. The message is labeled with the `«create»` stereotype. Can also be written as `cmessage`.
destroy_message(from_object,to_object);
  Sends a message labeled with the `«destroy»` stereotype from the from_object to the to_object. The object to_object is marked as destroyed, with an X at the end of its lifeline. The object's lifeline need not be otherwise completed. Can also be written as `dmessage`.
active(object);
  Changes the object's status to active, and changes its lifeline drawing style correspondingly. An active call in an already active object will result in a swimlane showing a nested object activation.
inactive(object);
  Changes the object's status to inactive, and changes its lifeline drawing style correspondingly. An inactive call on a nested object invocation will result in showing a simple active swimlane.
delete(object);
  The object deletes itself, drawing an X at the end of its lifeline. The object's lifeline need not be otherwise completed.
lifeline_constraint(object,label);
  Displays a constraint label (typically given inside curly braces) for the given object. The constraint will appear on the right of the object's lifeline at the time it appears. Can also be used to place an message label on the left of a message arrow, rather than its center. Can also be written as `lconstraint`.
lconstraint_below(object,label);
  same as `lconstraint`, but it will be shown below the current line instead of above.
object_constraint(label)
  Displays an object constraint (typically given inside curly braces) for the last object defined. Can also be written as `oconstraint`.
step();
  Steps the time by a single increment, extending all lifelines.
async();
  All subsequent messages are asynchronous and will be drawn correspondingly.
sync();
  All subsequent messages are synchronous and will be drawn correspondingly.
begin_frame(left_object,name,label_text);
  Begins a frame with the upper left corner at `left_object` column and the current line. The specified `label_text` is shown in the upper left corner.
end_frame(right_object,name);
  Ends a frame with the lower right corner at `right_object` column and the current line. The name must correspond to a `begin_frame`'s name.
comment(object,[name],[line_movement],[box_size] text);
  Displays a comment about the object. The name can be used with `connect_to_comment(object2,name);` to get additional connecting lines to the comment. `line_movement` changes the position of the comment and `box_size` its size. Note that there's no comma between `box_size` and `text`. `text` is the (multiline) comment-text that will be displayed. `name`, `line_movement` and `box_size` are optional (but the commas must still appear).
connect_to_comment(object2,name);
  See `comment`.