Group elements to avoid "hidden arrows"

[aheil]

To meet the original examples from the book, there is one way of annotating groups of messages like in the following example:

HIDE_STEREOTYPES()

Message(newOrder, "New order")
Message(item1, "Item 1")
Message(item2, "Item 2")
Splitter(splitter, "Splitter")

Send(newOrder, splitter)
Send(splitter, item1)
Send(splitter, item2) #transparent

The #transaprent tag should be avoided as it is a technical detail which should be hidden from the user in EIP-PlantUML.