On the page http://hl7.org/fhir/R4/terminologies.html#example, there is an explanation of the four binding types, 4.1.51 Required, 4.1.5.2 Extensible, 4.1.5.3 Preferred, and 4.1.5.3.2 Example Bindings.

But, this puts the Example Bindings section as a sub-section of the Preferred Binding section. It should start its own section as 4.1.5.4.