diff --git a/spec/ttml2.xml b/spec/ttml2.xml
index 48bc99878..5f9c56a37 100644
--- a/spec/ttml2.xml
+++ b/spec/ttml2.xml
@@ -2099,8 +2099,12 @@ declared to apply to the document instance<
The phrase mandatory semantics refers to all explicit use of the conformance
key phrases must and must not as well as any
-declarative statement that can be reasonably inferred from such key phrases. For example, these
-mandatory semantics include support for all features marked as mandatory in .
+declarative statement that can be reasonably inferred from such key phrases.
+
+
+Support for the mandatory semantics of a feature or
+extension applies only when the feature or
+extension is supported by a TTML content processor.
-
@@ -2110,8 +2114,7 @@ then it does so in a manner consistent with the defined semantics.
The phrase optional semantics refers to all explicit use of the conformance
key phrases should, should not,
may, and may not,
-as well as any declarative statement that can be reasonably inferred from such key phrases. For example, these
-optional semantics include support for all features marked as optional in .
+as well as any declarative statement that can be reasonably inferred from such key phrases.
@@ -19052,8 +19055,9 @@ is defined by .
This appendix is normative.
This appendix specifies (1) a set of feature designations, each of which
labels one or more syntactic and/or semantic features defined by this
-specification, and (2) for each designated feature, whether the feature is mandatory
-or optional for a transformation or presentation processor.
+specification, and (2) for each designated feature, whether the feature is mandatory or optional for a
+TTML content processor that complies with the requirements of
+ or .
A TTML processor is said to implement the transformation semantics or
implement the presentation semantics of feature designation F
@@ -22203,7 +22207,8 @@ enumerates every defined feature designation (expressed without the TT
Feature Namespace), and, for each designated feature, specifies
(1) the version of TTML in which the feature designation is first defined, and (2)
whether the designated feature must be implemented, i.e., is mandatory (M), or may be implemented, i.e.,
-is optional (O), for transformation and presentation processors.
+is optional (O), for a TTML content processor that complies with the requirements of
+ or .
In some cases, a new feature designation is defined in this (or a later) version of this specification that wasn't previously defined, and yet
the underlying functional feature so designated was previously defined by an earlier version. For example, the #padding-region
@@ -23650,7 +23655,8 @@ is optional (O), for transformation and , enumerates all
-mandatory features for a TTML transformation processor, providing additional
+mandatory features for a TTML content processor that complies with the requirements of
+, providing additional
comments to summarize the context of usage or the nature of the feature.
The profile definition document that defines the corresponding
TTML Transformation Profile is specified in
@@ -23742,7 +23748,8 @@ TTML Transformation Profile is specified in
For the sake of convenience, the following table,
, enumerates all
-mandatory features for a TTML presentation processor, providing additional
+mandatory features for a TTML content processor that complies with the requirements of
+, providing additional
comments to summarize the context of usage or the nature of the feature.
The profile definition document that defines the corresponding
TTML Presentation Profile is specified in