feat: Explicitly fills lxml.sax class methods and attributes

Make private variables available (for debug), and some methods are actually not compatible to base xml.sax.handler class

lxml-stubs/sax.pyi

@@ -1,33 +1,67 @@
 from typing import Generic, overload
 from xml.sax.handler import ContentHandler
 
-from ._types import _ElementFactory, _ElementOrTree, _ET_co
-from .etree import LxmlError, _ElementTree
+from ._types import _ET, SupportsLaxedItems, Unused, _ElementFactory, _ElementOrTree
+from .etree import LxmlError, _ElementTree, _ProcessingInstruction
 
 class SaxError(LxmlError): ...
 
 # xml.sax.handler is annotated in typeshed since Sept 2023.
-# For brevity, only properties and methods
-# not present in superclass are listed here.
-class ElementTreeContentHandler(Generic[_ET_co], ContentHandler):
+class ElementTreeContentHandler(Generic[_ET], ContentHandler):
+    _root: _ET | None
+    _root_siblings: list[_ProcessingInstruction]
+    _element_stack: list[_ET]
+    _default_ns: str | None
+    _ns_mapping: dict[str | None, list[str | None]]
+    _new_mappings: dict[str | None, str]
+    # Not adding _get_etree(), already available as public property
     @overload
     def __new__(
-        cls, makeelement: _ElementFactory[_ET_co]
-    ) -> ElementTreeContentHandler[_ET_co]: ...
+        cls, makeelement: _ElementFactory[_ET]
+    ) -> ElementTreeContentHandler[_ET]: ...
     @overload
     def __new__(cls, makeelement: None = None) -> ElementTreeContentHandler: ...
     @property
-    def etree(self) -> _ElementTree[_ET_co]: ...
+    def etree(self) -> _ElementTree[_ET]: ...
 
-class ElementTreeProducer:
+    # Incompatible method overrides; some args are similar
+    # but use other structures or names
+    def startElementNS(  # pyright: ignore[reportIncompatibleMethodOverride]
+        self,
+        ns_name: tuple[str, str],
+        qname: Unused,
+        attributes: SupportsLaxedItems[tuple[str | None, str], str] | None = None,
+    ) -> None: ...
+    def endElementNS(  # pyright: ignore[reportIncompatibleMethodOverride]
+        self,
+        ns_name: tuple[str, str],
+        qname: Unused,
+    ) -> None: ...
+    def characters(  # pyright: ignore[reportIncompatibleMethodOverride]
+        self,
+        data: str,
+    ) -> None: ...
+    def startElement(  # pyright: ignore[reportIncompatibleMethodOverride]
+        self,
+        name: str,
+        attributes: SupportsLaxedItems[str, str] | None = None,
+    ) -> None: ...
+    ignorableWhitespace = characters  # type: ignore[assignment]
+
+class ElementTreeProducer(Generic[_ET]):
+    _element: _ET
+    _content_handler: ContentHandler
+    # The purpose of _attr_class and _empty_attributes is
+    # more like a shortcut. These attributes are constant and
+    # doesn't help debugging
     def __init__(
         self,
-        element_or_tree: _ElementOrTree,
+        element_or_tree: _ElementOrTree[_ET],
         content_handler: ContentHandler,
     ) -> None: ...
     def saxify(self) -> None: ...
 
-# = ElementTreeProducer(args).saxify()
+# equivalent to saxify() in ElementTreeProducer
 def saxify(
     element_or_tree: _ElementOrTree,
     content_handler: ContentHandler,