add glossary

docs/asciidoc/modules/ROOT/partials/glossary.adoc → docs/asciidoc/modules/ROOT/pages/glossary.adoc

+= Glossary of Terms
+
+[caption="Work in Progress"]
+CAUTION: This glossary is a work in progress.
+It does not include all the terms in AsciiDoc.
+
+attribute reference:: An expression for dereferencing the value of a document attribute.
+
 admonition:: a callout paragraph or block that has a label or icon indicating its priority.
 
 backend:: a moniker for the expected output format; used as a key to select which converter to use; often used interchangeably with the name of a converter (i.e., the "html5" backend").

docs/asciidoc/modules/attributes/nav-ref.adoc

-* Reference Tables
+* Reference
 ** xref:ref-environment.adoc[]
 ** xref:ref-document.adoc[]
 ** xref:ref-character-replacement.adoc[]
+** xref:ROOT:glossary.adoc[]