diff --git a/parser/func.go b/parser/func.go
index feb5d13..b42fe0e 100644
--- a/parser/func.go
+++ b/parser/func.go
@@ -186,12 +186,12 @@ func (parser *ParsingOperation) parseFuncArguments (
 				err = parser.nextToken()
 				if err != nil { return }
 
-				output.defaultValue, err =
+				output.value, err =
 					parser.parseInitializationValues(1)
 				into.outputs = append(into.outputs, output)
 				if err != nil { return }
 			} else {
-				output.defaultValue, err =
+				output.value, err =
 					parser.parseArgument()
 				into.outputs = append(into.outputs, output)
 				if err != nil { return }
diff --git a/parser/node-traits.go b/parser/node-traits.go
index 29e64ce..4a3f66e 100644
--- a/parser/node-traits.go
+++ b/parser/node-traits.go
@@ -52,7 +52,19 @@ type permissionable struct {
 	permission types.Permission
 }
 
+// Permission returns the permision of the node.
 func (trait permissionable) Permission () (permission types.Permission) {
 	permission = trait.permission
 	return
 }
+
+// valuable allows a node to have an argument value.
+type valuable struct {
+	value Argument
+}
+
+// Value returns the value argument of the node.
+func (trait valuable) Value () (value Argument) {
+	value = trait.value
+	return
+}
diff --git a/parser/objt.go b/parser/objt.go
index 8e40715..ca72df4 100644
--- a/parser/objt.go
+++ b/parser/objt.go
@@ -109,11 +109,11 @@ func (parser *ParsingOperation) parseObjtMember () (
 		err = parser.nextToken()
 		if err != nil { return }
 
-		member.defaultValue,
+		member.value,
 		err = parser.parseInitializationValues(1)
 		if err != nil { return }
 	} else {
-		member.defaultValue, err = parser.parseArgument()
+		member.value, err = parser.parseArgument()
 		if err != nil { return }
 
 		err = parser.expect(lexer.TokenKindNewline)
diff --git a/parser/tree-tostring.go b/parser/tree-tostring.go
index 6ef1978..ebd080d 100644
--- a/parser/tree-tostring.go
+++ b/parser/tree-tostring.go
@@ -312,16 +312,16 @@ func (section *TypeSection) ToString (indent int) (output string) {
 		section.what.ToString())
 
 	isComplexInitialization :=
-		section.defaultValue.kind == ArgumentKindObjectInitializationValues ||
-		section.defaultValue.kind == ArgumentKindArrayInitializationValues
+		section.value.kind == ArgumentKindObjectInitializationValues ||
+		section.value.kind == ArgumentKindArrayInitializationValues
 
-	if section.defaultValue.value == nil {
+	if section.value.value == nil {
 		output += "\n"
 	} else if isComplexInitialization {
 		output += "\n"
-		output += section.defaultValue.ToString(indent + 1, true)
+		output += section.value.ToString(indent + 1, true)
 	} else {
-		output += " " + section.defaultValue.ToString(0, false)
+		output += " " + section.value.ToString(0, false)
 		output += "\n"
 	}
 	return
@@ -339,16 +339,16 @@ func (member ObjtMember) ToString (indent int) (output string) {
 	}
 	
 	isComplexInitialization :=
-		member.defaultValue.kind == ArgumentKindObjectInitializationValues ||
-		member.defaultValue.kind == ArgumentKindArrayInitializationValues
+		member.value.kind == ArgumentKindObjectInitializationValues ||
+		member.value.kind == ArgumentKindArrayInitializationValues
 	
-	if member.defaultValue.value == nil {
+	if member.value.value == nil {
 		output += "\n"
 	} else if isComplexInitialization {
 		output += "\n"
-		output += member.defaultValue.ToString(indent + 1, true)
+		output += member.value.ToString(indent + 1, true)
 	} else {
-		output += " " + member.defaultValue.ToString(0, false)
+		output += " " + member.value.ToString(0, false)
 		output += "\n"
 	}
 
@@ -473,8 +473,8 @@ func (block Block) ToString (indent int) (output string) {
 
 func (funcOutput FuncOutput) ToString () (output string) {
 	output += funcOutput.Declaration.ToString()
-	if funcOutput.defaultValue.kind != ArgumentKindNil {
-		output += " " + funcOutput.defaultValue.ToString(0, false)
+	if funcOutput.value.kind != ArgumentKindNil {
+		output += " " + funcOutput.value.ToString(0, false)
 	}
 	return
 }
diff --git a/parser/tree.go b/parser/tree.go
index d726cbf..98cf23e 100644
--- a/parser/tree.go
+++ b/parser/tree.go
@@ -161,8 +161,7 @@ type TypeSection struct {
 	nameable
 	typeable
 	permissionable
-	
-	defaultValue Argument
+	valuable
 }
 
 // ObjtMember represents a part of an object type definition.
@@ -171,9 +170,9 @@ type ObjtMember struct {
 	nameable
 	typeable
 	permissionable
+	valuable
 	
 	bitWidth     uint64
-	defaultValue Argument
 }
 
 // ObjtSection represents an object type definition.
@@ -190,7 +189,7 @@ type ObjtSection struct {
 type EnumMember struct {
 	locatable
 	nameable
-	value Argument
+	valuable
 }
 
 // EnumSection represents an enumerated type section.
@@ -262,7 +261,7 @@ type Block []Phrase
 // that it can have a default value.
 type FuncOutput struct {
 	Declaration
-	defaultValue Argument
+	valuable
 }
 
 // FuncSection represents a function section.
diff --git a/parser/type.go b/parser/type.go
index 5c484f2..a00c8e7 100644
--- a/parser/type.go
+++ b/parser/type.go
@@ -38,10 +38,10 @@ func (parser *ParsingOperation) parseTypeSection () (
 		err = parser.nextToken()
 		if err != nil { return }
 
-		section.defaultValue, err = parser.parseInitializationValues(0)
+		section.value, err = parser.parseInitializationValues(0)
 		if err != nil { return }
 	} else {
-		section.defaultValue, err = parser.parseArgument()
+		section.value, err = parser.parseArgument()
 		if err != nil { return }
 
 		err = parser.expect(lexer.TokenKindNewline)