Clarify the difference between Direct and Hierarchical policies

Signed-off-by: Nick Young <nick@isovalent.com>

site-src/references/policy-attachment.md

@@ -32,8 +32,19 @@ Individual policy APIs must
 - can be included in the Gateway API API group and installation or be defined by
   implementations
 - and must include a common `TargetRef` struct in their specification to identify
-  how and where to apply that policy, along with a field that indicates if
-  the reference is `Direct` or `Hierarchical`. (Shorter name suggestions welcomed)
+  how and where to apply that policy.
+- Hierarchical policies must include one of:
+  - a `defaults` stanza indicating which settings should flow across a hierarchy
+    and be defaulted
+  - an `overrides` stanza indicating which settings should flow across a hierarchy
+    and be overridden.
+
+If a policy CRD has a `targetRef` stanza, but _does not_ have either a
+`defaults` stanza, `overrides` stanza, or both, then it is a Direct Attachment Policy.
+
+If a policy CRD has a `targetRef` stanza, and _does_ have either a `defaults` stanza,
+an `overrides` stanza, or both, then it is a Hierarchical Attachment Policy, and
+its settings will flow over multiple objects.
 
 For Hierarchical Policies, this document also describes a set of expected behaviors
 for how settings can flow across a defined hierarchy.
@@ -178,7 +189,6 @@ spec:
         includeProtocol: true
         includeQueryString: true
   targetRef:
-    type: hiearchical
     kind: Gateway
     name: example
 ---
@@ -224,23 +234,26 @@ kind: RetryPolicy
 metadata:
   name: foo
 spec:
-  default:
-    maxRetries: 5
+  maxRetries: 5
   targetRef:
-    type: direct
     group: networking.example.net
     kind: ExternalService
     name: foo.com
 ```
 
+Because this CRD does _not_ have a `defaults` or `overrides` section, it is
+a Direct Attached Policy.
+
 ### Conflict Resolution
 It is possible for multiple policies to target the same resource. When this
 happens, merging is the preferred outcome. If multiple policy resources target
 the same resource _and_ have an identical field specified with different values,
 precedence MUST be determined in order of the following criteria, continuing on
 ties:
 
-* Hierarchical Policies override Direct Policies.
+* Direct Policies override Hierarchical Policies. If preventing settings from
+  being overwritten is important, implementations should only use Hierarchical
+  Policies, and the `override` stanza that implies.
 * The oldest Policy based on creation timestamp. For example, a Policy with a
   creation timestamp of "2021-07-15 01:02:03" is given precedence over a Policy
   with a creation timestamp of "2021-07-15 01:02:04".