He talks about the engineer as the person who sees himself as the center of his own discourse, the origin of his own language. The liberal humanist is usually an engineer in this respect. It provides a way to think without establishing a new center, a subject, a privileged reference, an origin. Derrida reads Levi-Strauss' discussion of myth in The Raw and the Cooked as a kind of bricolage on p. 89. You also can't do it if there are 14 kids all running around all over the place.
All systems fall on a continuum between the two.
Don't worry about this part. We'll settle for understanding the basic ideas about center and play. Something is fully present when it's stable and fixed, not provisional and mobile. Play is the disruption of presence. Or you can play along, rejoice in multiplicity and affirm the provisional nature of all meaning.