This most likely sneaked in as a copy paste error from GTK+
reference docs as g-i never had a object_grouped.sgml...
https://bugzilla.gnome.org/show_bug.cgi?id=688418
<!ENTITY % local.common.attrib "xmlns:xi CDATA #FIXED 'http://www.w3.org/2003/XInclude'">
<!ENTITY version SYSTEM "version.xml">
]>
-<!--ENTITY index-Objects-Grouped SYSTEM "objects_grouped.sgml"-->
<book id="index" xmlns:xi="http://www.w3.org/2003/XInclude">
<bookinfo>
<title>GObject Introspection Reference Manual</title>
<!ENTITY % local.common.attrib "xmlns:xi CDATA #FIXED 'http://www.w3.org/2003/XInclude'">
<!ENTITY version SYSTEM "version.xml">
]>
-<!--ENTITY index-Objects-Grouped SYSTEM "objects_grouped.sgml"-->
<refentry id="gi-overview">
<refmeta>
<refentrytitle role="top_of_page" id="gi-overview.top_of_page">Introspection Overview</refentrytitle>
<!ENTITY % local.common.attrib "xmlns:xi CDATA #FIXED 'http://www.w3.org/2003/XInclude'">
<!ENTITY version SYSTEM "version.xml">
]>
-<!--ENTITY index-Objects-Grouped SYSTEM "objects_grouped.sgml"-->
<refentry id="gi-struct-hierarchy">
<refmeta>
<refentrytitle role="top_of_page" id="gi-struct-hierarchy.top_of_page">Struct hierarchy</refentrytitle>