I have recently learned that doc-files/**/*.html files are treated as OVERVIEW files:

src/java.base/share/classes/java/net/doc-files/net-properties.html:47: warning: Tag @systemProperty cannot be used in overview documentation. It can only be used in the following types of documentation: module, package, class/interface, constructor, field, method.
<LI><P><B>{@systemProperty java.net.preferIPv4Stack}</B> (default: false)<BR>
^

This is because of this code:

                    @Override
                    public Void visitUnknown(Element e, Void p) {
                        if (utils.isOverviewElement(e) && !taglet.inOverview()) {
                            printTagMisuseWarn(utils.getCommentHelper(e), taglet, tag, "overview");
                        }
                        return null;
                    }
...

    public boolean isOverviewElement(Element e) {
        return e.getKind() == ElementKind.OTHER;
    }

While it might be impractical to introduce a new location to cover other documentation, such as doc-files/**/*.html, a clarification to the existing Taglet.Location.OVERVIEW might be a better alternative. The suggestion is as follows:

--- a/src/jdk.javadoc/share/classes/jdk/javadoc/doclet/Taglet.java
+++ b/src/jdk.javadoc/share/classes/jdk/javadoc/doclet/Taglet.java
@@ -147,7 +147,7 @@ public interface Taglet {
      * The kind of location in which a tag may be used.
      */
     enum Location {
- /** In an Overview document. */
+ /** In an Overview and other documentation. */
         OVERVIEW,


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Please keep in mind that this bug might not be easily reproducible after JDK-8288524.