Issue #17902: Clarify doc of ElementTree.iterparse
diff --git a/Doc/library/xml.etree.elementtree.rst b/Doc/library/xml.etree.elementtree.rst
index 45a0e7b..00cdacd 100644
--- a/Doc/library/xml.etree.elementtree.rst
+++ b/Doc/library/xml.etree.elementtree.rst
@@ -384,7 +384,8 @@
and ``"end-ns"`` (the "ns" events are used to get detailed namespace
information). If *events* is omitted, only ``"end"`` events are reported.
*parser* is an optional parser instance. If not given, the standard
- :class:`XMLParser` parser is used. Returns an :term:`iterator` providing
+ :class:`XMLParser` parser is used. *parser* can only use the default
+ :class:`TreeBuilder` as a target. Returns an :term:`iterator` providing
``(event, elem)`` pairs.
.. note::