The basic diagram generated by websequencediagram.com has the title centered without the frame.
But according to specification every diagram is placed inside a frame with title in it's left upper corner in a small rectangle with cutted edge. See:
Also it has a prefix "sd" to differentiate if from other kinds of diagrams. For instance a class diagram has a prefix "cd".
See: http://de.wikipedia.org/wiki/Sequenzdiagramm ("Das Schlüsselwort im Kopfbereich ist bei einem Sequenzdiagramm
If we do so we will be available to have the same drawing logic for any kinds of frames.
Question: Are we going to follow classic sequence diagram box with edge frame or are we going to stick with simple centered title?