+# Search in class or module hierarchy of a `MEntity`.
+#
+# It actually searches for pages about the mentity and extracts the
+# pre-calculated hierarchies by the `doc_post` phase.
+abstract class HierarchiesQuery
+ super DocQuery
+
+ redef fun make_results(nitx, results) do
+ var page = new DocPage("hierarchy", "Hierarchy")
+ for result in results do
+ if not result isa PageMatch then continue
+ var rpage = result.page
+ if not rpage isa MClassPage then continue
+ page.root.add_child build_article(rpage)
+ end
+ return page
+ end
+
+ # Build an article containing the hierarchy list depending on subclasses.
+ private fun build_article(page: MClassPage): DocArticle is abstract
+end
+
+# List all parents of a `MClass`.
+class AncestorsQuery
+ super HierarchiesQuery
+
+ redef fun build_article(page) do
+ return new MEntitiesListArticle(
+ "ancerstors",
+ "Ancestors for {page.mentity.name}",
+ page.ancestors.to_a)
+ end
+end
+
+# List direct parents of a `MClass`.
+class ParentsQuery
+ super HierarchiesQuery
+
+ redef fun build_article(page) do
+ return new MEntitiesListArticle(
+ "parents",
+ "Parents for {page.mentity.name}",
+ page.parents.to_a)
+ end
+end
+
+# List direct children of a `MClass`.
+class ChildrenQuery
+ super HierarchiesQuery
+
+ redef fun build_article(page) do
+ return new MEntitiesListArticle(
+ "children",
+ "Children for {page.mentity.name}",
+ page.children.to_a)
+ end
+end
+
+# List all descendants of a `MClass`.
+class DescendantsQuery
+ super HierarchiesQuery
+
+ redef fun build_article(page) do
+ return new MEntitiesListArticle(
+ "descendants",
+ "Descendants for {page.mentity.name}",
+ page.children.to_a)
+ end
+end
+