It doesn't understand what you are typing. It probably just splits on words and tries to match what it has seen before. I'll bet if you abuse it you can break it.

Edit: It seems to do a split on spaces and then takes the first word and the last word as the nodes and labels the edge with what is in the middle.

http://diagrammr.com/edit?key=dkCDRHJUJA7

note: The diagrams are not locked in any way so my carefully crafted test is no longer there.

it was something along the lines of

  a b c
  a c d
  d ef g