diff --git a/IPython/core/formatters.py b/IPython/core/formatters.py
index 51553a1..19c519b 100644
--- a/IPython/core/formatters.py
+++ b/IPython/core/formatters.py
@@ -449,6 +449,10 @@ class HTMLFormatter(BaseFormatter):
objects, define a :meth:`_repr_html_` method or use the :meth:`for_type`
or :meth:`for_type_by_name` methods to register functions that handle
this.
+
+ The return value of this formatter should be a valid HTML snippet that
+ could be injected into an existing DOM. It should *not* include the
+ ````` or ```
`` tags.
"""
format_type = Str('text/html')
@@ -462,6 +466,10 @@ class SVGFormatter(BaseFormatter):
objects, define a :meth:`_repr_svg_` method or use the :meth:`for_type`
or :meth:`for_type_by_name` methods to register functions that handle
this.
+
+ The return value of this formatter should be valid SVG enclosed in
+ ```