MessageArea Properties 
firstVisibleMessage
First visible message.
Caution
Note that this property is not API-visible, that means it cannot be changed by application developers.
historyVisible
Visibility of the whole message history.
Both users and administrators can personalize this property.
In personalization this property can be assigned the value false.
Note
This property can currently only be programmed in the source code.
maxVisibleMessages
The maximum number of messages that can be displayed without the scrollbar. A negative or null value means "unlimited" and displays all the messages without the scrollbar.
Note
This property can currently only be programmed in the source code.