diff --git a/subscriptions/spec.md b/subscriptions/spec.md
index 1b9b4e49f..41162d5a2 100644
--- a/subscriptions/spec.md
+++ b/subscriptions/spec.md
@@ -756,10 +756,12 @@ When encoded in JSON, a filter is encoded as follows:
 { "dialect URI-Reference" : { <dialect-specific-properties> } }
 ```
 
-This specification defines the following 7 filter dialects that all
-implementations MUST support:
+###### 3.2.4.1.1 REQUIRED Filter Dialects
 
-###### `exact` filter dialect
+This specification defines the following 6 filter dialects that MUST be 
+supported by every implementation:
+
+**`exact`**
 
 The keys are the names of the CloudEvents attributes to be matched,
 and their values are the String values to use in the comparison.
@@ -775,7 +777,7 @@ For example:
 { "exact": { "type": "com.github.push", "subject": "https://github.com/cloudevents/spec" } }
 ```
 
-###### `prefix` filter dialect
+**`prefix`**
 
 The keys are the names of the CloudEvents attributes to be matched,
 and their values are the String values to use in the comparison.
@@ -791,7 +793,7 @@ For example:
 { "prefix": { "type": "com.github.", "subject": "https://github.com/cloudevents" } }
 ```
 
-###### `suffix` filter dialect
+**`suffix`**
 
 The keys are the names of the CloudEvents attributes to be matched,
 and their values are the String values to use in the comparison.
@@ -807,7 +809,7 @@ For example:
 { "suffix": { "type": ".created", "subject": "/cloudevents/spec" } }
 ```
 
-###### `all` filter dialect
+**`all`**
 
 Use of this MUST include a nested array of filter expressions, where all
 nested filter expressions MUST evaluate to true in order for the `all`
@@ -826,10 +828,10 @@ For example:
 }
 ```
 
-###### `any` filter dialect
+**`any`**
 
-Use of this MUST include one nested array of filter expressions, where at least
-one nested filter expressions MUST evaluate to true in order for the `any`
+Use of this MUST include one nested array of filter expressions, where at 
+least one nested filter expressions MUST evaluate to true in order for the `any`
 filter expression to be true.
 
 Note: there MUST be at least one filter expression in the array.
@@ -845,9 +847,10 @@ For example:
 }
 ```
 
-###### `not` filter dialect
+**`not`**
 
-Use of this MUST include one nested filter expression, where the result of this
+Use of this MUST include one nested filter expression, where the result of 
+this
 filter expression is the inverse of the result of the nested expression.
 In other words, if the nested expression evaluated to true, then the `not`
 filter expression's result is false.
@@ -860,14 +863,22 @@ For example:
 }
 ```
 
-###### `sql` filter dialect
+###### 3.2.4.1.2 OPTIONAL Filter Dialects
+
+The support of the following dialects are OPTIONAL for implementations of
+this specification: 
+
+**`sql`**
 
-Use of this MUST have a string value, representing a [CloudEvents SQL Expression](../cesql/spec.md).
-The filter result MUST be true if the result value of the expression, coerced to boolean, equals to the `TRUE` boolean value,
+Use of this MUST have a string value, representing a [CloudEvents SQL 
+Expression](../cesql/spec.md).
+The filter result MUST be true if the result value of the expression, 
+coerced to boolean, equals to the `TRUE` boolean value,
 otherwise MUST be false if an error occurred while evaluating the expression or if the result value,
 coerced to boolean, equals to the `FALSE` boolean value.
 
-Implementations SHOULD reject subscriptions with invalid CloudEvents SQL expressions.
+Implementations SHOULD reject subscriptions with invalid CloudEvents SQL 
+expressions.
 
 For example: