diff --git a/schema/CreativeWork.schema.yaml b/schema/CreativeWork.schema.yaml
index a94d443b8f..ab8fc5fd1e 100644
--- a/schema/CreativeWork.schema.yaml
+++ b/schema/CreativeWork.schema.yaml
@@ -29,3 +29,7 @@ properties:
       anyOf:
         - $ref: URL.schema.yaml
         - $ref: CreativeWork.schema.yaml
+  text:
+    '@id': schema:text
+    description: The textual content of this CreativeWork.
+    type: string
diff --git a/schema/MediaObject.schema.yaml b/schema/MediaObject.schema.yaml
index c416bb597d..f4e63ee49b 100644
--- a/schema/MediaObject.schema.yaml
+++ b/schema/MediaObject.schema.yaml
@@ -10,5 +10,5 @@ properties:
   contentUrl:
     '@id': schema:contentUrl
     description: Actual bytes of the media object, for example the image file or video file.
-    anyOf:
+    allOf:
       - $ref: URL.schema.yaml
diff --git a/schema/Thing.schema.yaml b/schema/Thing.schema.yaml
index af01123b57..8b85d280c1 100644
--- a/schema/Thing.schema.yaml
+++ b/schema/Thing.schema.yaml
@@ -6,9 +6,11 @@ description: The most generic type of item https://schema.org/Thing.
 type: object
 properties:
   type:
-    # Note: this is a special property analagous to JSON-LD's `@type` keyword
+    # This is a special property analagous to JSON-LD's `@type` keyword
     # and so should not have a `@id` since it is not a property.
-    description: The name of the type
+    # It is extended with the titles of all descendant types during
+    # the generation of schema.json files.
+    description: The name of the type and all descendant types.
     type: string
     enum: [Thing]
   alternateNames:
@@ -25,5 +27,10 @@ properties:
     '@id': schema:name
     description: The name of the item.
     type: string
+  url:
+    '@id': schema:url
+    description: The URL of the item.
+    allOf:
+      - $ref: URL.schema.yaml
 required:
   - type
diff --git a/schema/software/Expression.schema.yaml b/schema/software/Expression.schema.yaml
index 9b8861764b..e17c905d62 100644
--- a/schema/software/Expression.schema.yaml
+++ b/schema/software/Expression.schema.yaml
@@ -2,7 +2,10 @@ title: Expression
 '@id': Expression
 $extends: SoftwareSourceCode.schema.yaml
 role: secondary
-status: Experimental
+status: experimental
 description: An expression.
 properties:
-  value: {}
+  value:
+    '@id': stencila:value
+    allOf:
+      - $ref: ../Node.schema.yaml
diff --git a/schema/software/SoftwareSourceCode.schema.yaml b/schema/software/SoftwareSourceCode.schema.yaml
index 10983307f8..2be575e0c4 100644
--- a/schema/software/SoftwareSourceCode.schema.yaml
+++ b/schema/software/SoftwareSourceCode.schema.yaml
@@ -10,7 +10,8 @@ properties:
     '@id': schema:codeRepository
     description: |
       Link to the repository where the un-compiled, human readable code and related code is located (SVN, github, CodePlex)
-    $ref: URL.schema.yaml
+    allOf:
+      - $ref: URL.schema.yaml
   codeSampleType:
     '@id': schema:codeSampleType
     description: |