/usr/share/gtk-doc/html/gtkglext is in libgtkglext1-doc 1.2.0-3.2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/gtk-doc/html/../../doc/libgtkglext1-doc/html/gtkglext
/usr/share/gtk-doc/html/../../doc/libgtkglext1-doc/html/gtkglext