Clarify attestation model vs. attestation type

Fixes #27, #28

index.src.html

@@ -781,8 +781,12 @@
 to a remote party. They differ in the details of how the attestation statement is laid out, and how its components are computed.
 The different attestation types are defined in [[#defined-attestation-types]].
 
-Attestation types are orthogonal to attestation models, i.e. attestation types in general are not restricted
-to a single attestation model.
+This specification also defines a number of attestation models. These define how a [RP] establishes trust in a particular
+attestation statement, after verifying that it is cryptographically valid.
+
+Attestation types are orthogonal to attestation models, i.e. attestation types in general are not restricted to a single
+attestation model. Broadly speaking, attestation types pertain to the syntax of the attestation statement, while attestation
+models pertain to the semantics.
 
 
 ### Attestation Models ### {#attestation-models}