The HTML exporter has delineations for preamble and postamble. The
default value for org-html-preamble is t, which makes the HTML
exporter insert the preamble. See the variable
org-html-preamble-format for the format string.
Set org-html-preamble to a string to override the default format
string. If set to a function, the HTML exporter expects the function
to return a string upon execution. The HTML exporter inserts this
string in the preamble. The HTML exporter does not insert a preamble
if org-html-preamble is set nil.
The above also applies to org-html-postamble and
org-html-postamble-format. In addition, org-html-postamble can be
set to auto (its default value), which makes the HTML exporter build
a postamble from looking up author’s name, email address, creator’s
name, and date.