If you plan to use the texinfo-multiple-files-update command,
the outer Texinfo file that lists included files within it should
contain nothing but the beginning and end parts of a Texinfo file, and
a number of @include commands listing the included files. It
should not even include indices, which should be listed in an included
file of their own.
Moreover, each of the included files must contain exactly one highest
level node (conventionally, @chapter or equivalent),
and this node must be the first node in the included file.
Furthermore, each of these highest level nodes in each included file
must be at the same hierarchical level in the file structure.
Usually, each is a @chapter, an @appendix, or an
@unnumbered node. Thus, normally, each included file contains
one, and only one, chapter or equivalent-level node.
The outer file should contain only one node, the ‘Top’ node. It
should not contain any nodes besides the single ‘Top’ node. The
texinfo-multiple-files-update command will not process
them.