bazel syntax: augment doc comment on symbol registry
RELNOTES: None
PiperOrigin-RevId: 239657747
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/Runtime.java b/src/main/java/com/google/devtools/build/lib/syntax/Runtime.java
index ea378ae..afaea44 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/Runtime.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/Runtime.java
@@ -168,6 +168,11 @@
* A registry of builtins, including both global builtins and builtins that are under some
* namespace.
*
+ * <p>The registry contains Starlark universal builtins (None, len, etc), core build-language
+ * functions (depset, select, glob, etc), members of the native module (FilesetEntry,
+ * local_repository, vardef, ...), but not the native rules (cc_library, etc) nor other built-ins
+ * (CcCompilationInfo, java_common.JavaRuntimeInfo, etc).
+ *
* <p>Concurrency model: This object is thread-safe. Read accesses are always allowed, while write
* accesses are only allowed before this object has been frozen ({@link #freeze}). Prior to
* freezing, all operations are synchronized, while after freezing they are lockless.
