You can define the variable PRE_BODY_CLOSE to add text just
before the HTML </body> element. Nothing is added by default.
If PROGRAM_NAME_IN_FOOTER is set, the date and name of the
program that generated the output are output in the footer.
The customization variables JS_WEBLABELS and JS_WEBLABELS_FILE
are also used in the page footer formatting. See HTML Customization
Variables in Texinfo.
The format_end_file function reference give full control over the page
footer formatting done at the bottom of each HTML output file.
$file_end format_end_file ($converter, $filename, \%tree_unit_element) ¶$filename is the name of the file output.
\%tree_unit_element is the last output unit of the file.
This function should print the page footer, including
the </body> element.