Interactions in Scribble are based on two assumptions:

• Asynchrony, so no wait on sends, and

• Message order preservation for messages sent to the same role
  The syntax for the interaction is:

<MessageSignature> [from <Role>] [ to <Role> ( "," <Role> )* )]

The following example shows a similar type of interaction as shown in the
'hello world' example.

Customer introduces Supplier;
Order from Customer to Supplier;

In this sample, two roles are declared, with the interaction indicating that
a message of type 'Order' will be sent from role 'Customer' to role 'Supplier'.

placeOrder(Order) from Customer to Supplier;

This example demonstrates an alternative way for the exchanged message to be
specified. In the first sample a message-style was used. In this sample, an
RPC style has been used, specifying the operation name with type parameters.
In this case, only a single typed parameter Order has
been specified, but this could be a comma separated list of one or more
types.