Included in content model of elements (56):

answer, appendix, appendix.class, article, article.class, bibliodiv, bibliography, blockquote, callout, caption, chapter, chapter.class, colophon, dedication, entry, glossary, glossdiv, highlights, index, itemizedlist, legalnotice, listitem, msgexplan, msgtext, orderedlist, para, partintro, preface, procedure, qandadiv, qandaset, question, refsect1, refsect2, refsect3, refsection, refsynopsisdiv, revdescription, sect1, sect2, sect3, sect4, sect5, section, section.class, setindex, sidebar, simplesect, step, taskprerequisites, taskrelated, tasksummary, td, textobject, th, variablelist

Substituted with elements (5):

caution, important, note, tip, warning

In model groups (12):

component.mix [ref], divcomponent.mix [ref], highlights.mix [ref], legalnotice.mix [ref], listpreamble.mix [ref], para.mix [ref], qandaset.mix [ref], refcomponent.mix [ref], revdescription.mix [ref], sidebar.mix [ref], tabentry.mix [ref], textobject.mix [ref]

As head element of substitution group affiliations (5):

caution, important, note, tip, warning