Reword description of default context again

adoc/chapters/programming_interface.adoc

@@ -969,12 +969,14 @@ The [code]#platform# class also provides constructors, but constructing a new
 [code]#platform# instance merely creates a new object that is a copy of one of
 the objects returned by [api]#platform::get_platforms#.
 
-Each platform has a default context which contains all of the devices in the
-platform and has no associated asynchronous error handler.
+Each platform has an associated default context which contains all of the
+devices in the platform.
+This default context does not have an asynchronous error handler.
 Applications can retrieve a copy of this default `context` object, for example,
 by constructing a `queue`.
 These copies follow the common reference semantics, as though they are all
-copies of a single internal `context` object that is held by each platform.
+copies of an internal per-platform `context` object representing the platform's
+default context.
 
 The [code]#platform# class provides the common reference semantics as defined in
 <<sec:reference-semantics>>.