For the purposes of airspeed restrictions within airspace, the FAA regulations list the following area description (emphasis mine):
No person may operate an aircraft in the airspace underlying a Class B airspace area designated for an airport [...] at an indicated airspeed of more than 200 knots (230 mph).
Should we understand the described airspace to be any and all airspace underlying a Class B where that specific Class B is designated for an airport? Or, should we understand the described airspace to be any and all airspace designated for an airport (Class C, D, or E) which is underlying a Class B?
Are there letters of interpretation or other regulations which clarify the grammatical ambiguity of this regulation?