Found:

Shape Component

MORPHOLOGY: a component in the grammar proposed in the work of Arnold Zwicky. This component contains the lexicon, together with separate sets of inflectional rules and derivational rules. Moreover, this component houses the Shape Conditions which govern the selection of different allomorphs postlexically, that is, in the syntax. EXAMPLE: the distribution of the English a/an allomorphs (a book vs. an apple) is handled by a Shape Condition.

LIT.	Zwicky, A. (1977)