org: HTML preamble and postamble

 
 12.6.3 HTML preamble and postamble
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 The HTML exporter lets you define a preamble and a postamble.
 
    The default value for ‘org-html-preamble’ is ‘t’, which means that
 the preamble is inserted depending on the relevant format string in
 ‘org-html-preamble-format’.
 
    Setting ‘org-html-preamble’ to a string will override the default
 format string.  If you set it to a function, it will insert the output
 of the function, which must be a string.  Setting to ‘nil’ will not
 insert any preamble.
 
    The default value for ‘org-html-postamble’ is ‘'auto’, which means
 that the HTML exporter will look for information about the author, the
 email, the creator and the date, and build the postamble from these
 values.  Setting ‘org-html-postamble’ to ‘t’ will insert the postamble
 from the relevant format string found in ‘org-html-postamble-format’.
 Setting it to ‘nil’ will not insert any postamble.