update-otags runs otags on the system-wide installed OCaml files (in ocamlc -where). This makes it
possible to use the tag-features of vi/vim and Emacs to jump to the declarations of library functions in
the system-wide installed .mli files to read the documentation that is hopefully embedded in those files.
To use the system-wide tags table in Emacs, use M-xvisit-tags-table<RET>/var/lib/otags/TAGS. To load
it by default, customize tags-table-list to contain /var/lib/otags (by using M-xcustomize-variable, for
instance).
For vim use :settags=/var/lib/otags/tags or add settags=/var/lib/otags/tags to your .vimrc.
One would typically update the system-wide tags tables with a cron-job once per week or day.