Lucariello, J. (1987).
Spinning fantasy: Themes, structure, and knowledge base.
Child Development. 58 (2), 434-442.

3 structural components in symbolic play: action, self-other relations (decentration), object substitutions (Piaget, 1962).

Garvey & Berndt (1977) and Nicolich (1977) add planfulness to this list, which is to organize pretense around a goal

Pretense themes are generally based on real, familiar events (Bretherton, 1984; Piaget, 1962).

Knowledge base is in the form of event schemas, which contain information about means and ends, inclusive of sequencing actions to reach ends, the specific context for actions, and knowledge of roles and actors in events. (Narrative theory; Nelson et al., 1983; Nelson & Gruendel, 1981)

Lucariello believes that with greater knowledge base, stored as more extensive event schemas, play would be more complex seen through greater planfulness, more substitutions, integrated action, and decentration regarding roles. Moms are usually scaffolding more complex play than the child is engaging in alone when in collaboration. In collaborative play when knowledge base is extensive, play skills should be more equalized. (Sample: 24 to 29 mos.)

He found that children could integrate action in event-based fantasies and mom provided more action integration in non-event based play.