diff --git a/platform/commonUI/about/README.md b/platform/commonUI/about/README.md
index da28ed68a7..05bcfe22cd 100644
--- a/platform/commonUI/about/README.md
+++ b/platform/commonUI/about/README.md
@@ -1,2 +1,26 @@
 The "about" bundle provides the default lower-right application logo,
-as well as the dialog it launches when clicked.
\ No newline at end of file
+as well as the dialog it launches when clicked.
+
+# Extensions
+
+The About dialog contains several line items to display different
+version properties (e.g. when built, et cetera.) Plug-ins may wish
+to introduce additional line items here, in particular if the
+platform is used to build a separately-branded piece of software.
+
+This bundle introduces the `versions` extension category to support this.
+An extension of this category is implementation-less (all information
+is contained within its declaration) and should include the following
+fields:
+
+* `name`: The name to display for this version line-item; this may
+  be the name of the software, or something else such as "Built".
+* `value`: The value to display corresponding to this line-item;
+  this is typically a version number, revision identifier, or
+  human-readable date.
+* `description`: Optional; a longer-form description of this line
+  item, to display in a tooltip.
+
+Ordering of these line items is handled by extension priority; see framework
+documentation (`platform/framework/README.md`) for information on how
+this ordering is handled.