put back references section

Signed-off-by: Lukas Jungmann <lukas.jungmann@oracle.com>

spec/src/main/asciidoc/spec.adoc

diff --git a/spec/src/main/asciidoc/spec.adoc b/spec/src/main/asciidoc/spec.adoc
index 07c2e7a..f7e7828 100644
--- a/spec/src/main/asciidoc/spec.adoc
+++ b/spec/src/main/asciidoc/spec.adoc
@@ -1209,3 +1209,23 @@
     // ...
 }
 ----
+
+== References
+
+Java SE,
+https://www.oracle.com/java/
+
+JSR 175: A Metadata Facility for the Java
+Programming Language. http://jcp.org/en/jsr/detail?id=175
+
+Jakarta EE Platform (Jakarta EE),
+https://jakarta.ee/specifications/platform/
+
+Jakarta Enterprise Beans,
+https://jakarta.ee/specifications/enterprise-beans/
+
+Jakarta Interceptors,
+https://jakarta.ee/specifications/interceptors/
+
+RFC 2119.
+http://www.faqs.org/rfcs/rfc2119.html
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