docs: add more infos to match conditions docs

Signed-off-by: Charles-Edouard Brétéché <[email protected]>

website/docs/policies/match-conditions.md

@@ -4,6 +4,10 @@ You can define match conditions if you need fine-grained request filtering.
 
 Match conditions are **CEL expressions**. All match conditions must evaluate to `true` for the request to be evaluated.
 
+!!!info
+
+    Match conditions have access to the same CEL variables as validation expressions.
+
 ## Example
 
 ```yaml
@@ -24,4 +28,13 @@ spec:
 In the policy above, the `matchConditions` will be used to deny all requests having the `x-force-deny` header.
 
 - If an incoming request doesn't have the `x-force-deny` header, then the condition will return `false` and the policy won't apply
-- If an incoming request has the `x-force-deny` header, then the condition will return `true` and the `deny` rule will deny the request with status code `403`
+- If an incoming request has the `x-force-deny` header, then the condition will return `true` and the `deny` rule will deny the request with status code `403`
+
+## Error handling
+
+In the event of an error evaluating a match condition the policy is not evaluated. Whether to reject the request is determined as follows:
+
+1. If any match condition evaluated to `false` (regardless of other errors), the policy is skipped.
+1. Otherwise:
+    - for `failurePolicy: Fail`, reject the request (without evaluating the policy).
+    - for `failurePolicy: Ignore`, proceed with the request but skip the policy.