Definition:Occurrence (Formal Systems)

Definition
Let $$\mathcal F$$ be a formal language.

Let $$S$$ be a string in the alphabet of $$\mathcal F$$.

Let $$\mathbf W$$ be a well-formed word of $$\mathcal F$$.

Each place where $$S$$ appears in $$\mathbf W$$ is called an occurrence of $$S$$ in $$\mathbf W$$.