Fix HTML 4

sphinx/transforms/post_transforms/__init__.py

@@ -231,7 +231,10 @@ def run(self, **kwargs: Any) -> None:
         # result in a "Losing ids" exception if there is a target node before
         # the only node, so we make sure docutils can transfer the id to
         # something, even if it's just a comment and will lose the id anyway...
-        process_collapsible_nodes(self.document, self.app.builder.name)
+        builder_name = self.app.builder.name
+        if getattr(self.app.builder.config, "html4_writer", False):
+            builder_name = "html4"
+        process_collapsible_nodes(self.document, builder_name)
 
 
 class SigElementFallbackTransform(SphinxPostTransform):

sphinx/writers/html.py

@@ -702,18 +702,6 @@ def visit_option_group(self, node: Element) -> None:
         super().visit_option_group(node)
         self.context[-2] = self.context[-2].replace(' ', ' ')
 
-    def visit_collapsible(self, node: Element) -> None:
-        self.body.append('<details>')
-
-    def depart_collapsible(self, node: Element) -> None:
-        self.body.append('</details>')
-
-    def visit_collapsible_summary(self, node: Element) -> None:
-        self.body.append('<summary>')
-
-    def depart_collapsible_summary(self, node: Element) -> None:
-        self.body.append('</summary>')
-
     # overwritten
     def visit_Text(self, node: Text) -> None:
         text = node.astext()