htmltoc adds a table of contents to the HTML document named on the command line or provided as standard
input. The table of contents is inserted between <tableofcontents> and </tableofcontents>, which must
appear on lines by themselves. Any text between those two markers is discarded. These markers are
inserted automatically by the sl2h(1) filter.
The table of contents includes only headers at levels 2, 3, 4, and 5. This can be changed by using a
command-line option, e.g., -123456789Ptoincludeallpossibleheaders.