Node:subsubsection, Next:Raise/lower sections, Previous:unnumberedsubsec appendixsubsec subheading, Up:Structuring
The fourth and lowest level sectioning commands in Texinfo are the `subsub' commands. They are:
@subsubsection
@subsection.)  In a printed manual,
subsubsection titles appear in the table of contents and are numbered
four levels deep.
@unnumberedsubsubsec
@appendixsubsubsec
@subsubheading
@subsubheading command may be used anywhere that you need
a small heading that will not appear in the table of contents.  In
Info, subsubheadings look exactly like ordinary subsubsection
headings. 
In Info,  `subsub' titles are underlined with periods. 
For example,
@subsubsection This is a subsubsection
produces
This is a subsubsection .......................