81dbfe30_essage_Sequence_Chart_Renderer__Meaning
[Source Attribute] label [Meaning] 
A label to place on the message arc, or label to use for an entity. This is reproduced literally above the message arc or in place of the entity name. When used as a message arc label this may also contain parameters or required text. If a \n is encountered, it will be interpreted as a newline, placing text below the arc as well as above it in the normal position, or expanding entity tiles onto more lines.
Mscgen: A Message Sequence Chart Renderer
Meaning