diff --git a/references.adoc b/references.adoc
index c40dd14..edc1b3f 100644
--- a/references.adoc
+++ b/references.adoc
@@ -2,6 +2,7 @@ References
 ~~~~~~~~~~
 .This Repository
 *  link:README.adoc[]
+*  link:schema/attributeClasses.adoc[Attribute Classes that can be used to categorize individual attributes]
 
 .External Links
 * https://spacetelescope.github.io/understanding-json-schema/UnderstandingJSONSchema.pdf[Understanding JSON Schema]; Good intro but somewhat dated: Refers to Draft 4, current is Draft 7