diff --git a/src/pvxs/server.h b/src/pvxs/server.h
index 4de9b84..6697a2c 100644
--- a/src/pvxs/server.h
+++ b/src/pvxs/server.h
@@ -40,10 +40,13 @@ struct Config;
  * In order to be useful, a Server will have one or more Source instances added
  * to it with addSource().
  *
- * As a convenience, each Server instance automatically contains a "builtin" StaticSource
+ * As a convenience, each Server instance automatically contains a "__builtin" StaticSource
  * to which SharedPV instances can be directly added.
- * The "builtin" has priority zero, and can be accessed or even removed like any Source
+ * The "__builtin" has priority zero, and can be accessed or even removed like any Source
  * explicitly added with addSource().
+ *
+ * There is also a "__server" source which provides the special "server" PV
+ * used by the pvlist CLI.
  */
 class PVXS_API Server
 {
@@ -80,16 +83,21 @@ public:
     //! Suitable for use in self-contained unit-tests.
     client::Config clientConfig() const;
 
-    //! Add a SharedPV to the "builtin" StaticSource
+    //! Add a SharedPV to the "__builtin" StaticSource
     Server& addPV(const std::string& name, const SharedPV& pv);
-    //! Remove a SharedPV from the "builtin" StaticSource
+    //! Remove a SharedPV from the "__builtin" StaticSource
     Server& removePV(const std::string& name);
 
     //! Add a Source to this server with an arbitrary source name.
     //!
+    //! Source names beginning with "__" are reserved for internal use.
+    //! eg. "__builtin" and "__server".
+    //!
     //! @param name Source name
     //! @param src The Source.  A strong reference to this Source which will be released by removeSource() or ~Server()
     //! @param order Determines the order in which this Source::onCreate() will be called.  Lowest first.
+    //!
+    //! @throws std::runtime_error If this (name, order) has already been added.
     Server& addSource(const std::string& name,
                       const std::shared_ptr<Source>& src,
                       int order =0);
diff --git a/src/server.cpp b/src/server.cpp
index 248f30f..4f67df9 100644
--- a/src/server.cpp
+++ b/src/server.cpp
@@ -42,7 +42,7 @@ Server::Server(const Config& conf)
     /* Here be dragons.
      *
      * We keep two different ref. counters.
-     * - "externel" counter which keeps a server running.
+     * - "external" counter which keeps a server running.
      * - "internal" which only keeps server storage from being destroyed.
      *
      * External refs are held as Server::pvt.  Internal refs are
@@ -405,8 +405,8 @@ Server::Pvt::Pvt(const Config &conf)
     // Add magic "server" PV
     {
         auto L = sourcesLock.lockWriter();
-        sources[std::make_pair(-1, "server")] = std::make_shared<ServerSource>(this);
-        sources[std::make_pair(-1, "builtin")] = builtinsrc.source();
+        sources[std::make_pair(-1, "__server")] = std::make_shared<ServerSource>(this);
+        sources[std::make_pair(-1, "__builtin")] = builtinsrc.source();
     }
 }