The universality of "single starting point"

Hi Folks,

1. Formal grammars require that a single symbol be the starting point for all productions. For example, the starting symbol is S in this grammar:

	S -> a Q a
	Q -> ...

2. Structured programming tells us that every function should have a single entry point.

3. XML has a single starting point - the root element

Wow! I see this concept of a single starting point everywhere I look. Above I have provided three occurrences. Would you provide other occurrences please?

/Roger