What's the passenger size range of a 135 aircraft?

FAA documents are so technical I can't find basic information about how many passengers a part 135 aircraft can carry.
Answers

Zaphod Beeblebrox

Title 14 CFR Part 119 determines which part of the FAR's an operator is required to operate under, which includes Part 121, 125 and Part 135. For Part 135 "on-demand" (non-scheduled) operations, and for limited scheduled operations where no route between any two points is flown more than 4 times per week, a non-turbojet aircraft having 30 passenger seats or less and a payload capacity of 7,500 pounds or less may be used. For scheduled operations where at least one route between any two points is flown 5 or more times per week (termed commuter operations) , then the operation is limited to a non-turbojet aircraft of 9 seats or less and 7,500 pounds payload capacity. Any scheduled service using a turbojet aircraft of any size is required to operate under Part 121 or Part 125.

JetDoc

14 CFR Part 135 does not specify a certain number of passenger seats for aircraft. The regulation covers the rules for certification and operation of a commercial air carrier.

Bill

Where do you find these terms part 121 and part 135? What do you know about them?