… the enhancing relation may be internal rather than external; that is, the β-clause may relate to the enactment of the proposition or proposal realised by the α-clause rather than to the figure that it represents. For example, if it is not too personal an inquiry, what limits do you set… means ‘if it is not…, I ask you…’; that is, the condition is on the act of questioning, not on the content of the question.
Monty Python's Life Of Brian provides an easy–to–remember instance:
If it's not a personal question, are you a virgin?
Note that English Text: System And Structure (Martin 1992) is a major source of confusion on the internal/external distinction (evidence here), as is Working With Discourse: Meaning Beyond The Clause (Martin & Rose 2007).