You can set the variable DOCTYPE to replace the default.
the DOCTYPE is output at the very beginning of each output
file.
You can define the variable EXTRA_HEAD to add text within the
<head> HTML element. Similarly, the value of
AFTER_BODY_OPEN is added just after <body> is output.
These variables are empty by default.
The <body> element attributes may be set by defining the
customization variable BODYTEXT.
By default, the encoding name from ENCODING_NAME is used. If
this variable is not defined, it is automatically determined.
A date is output in the header if DATE_IN_HEADER is set.
The description from @documentdescription (or a value set as a
customization variable) is used in the header
(see @documentdescription in Texinfo).
<link> elements are used in the header if USE_LINKS is
set, in which case LINKS_BUTTONS determines which links are
used and BUTTONS_REL determines the link type associated with
the rel attribute. See Simple Navigation Panel Customization.
You can set HTML_ROOT_ELEMENT_ATTRIBUTES to add attributes to
the <html> element.
The customization variables
SECTION_NAME_IN_TITLE,
PACKAGE_AND_VERSION, PACKAGE_URL and other similar variables,
HTML_MATH and INFO_JS_DIR
may also be used to change the page header formatting.
See HTML Customization Variables in Texinfo.
The following function references give full control over the page header formatting done at the top of each HTML output file.
$file_begin format_begin_file ($converter, $filename, \%tree_unit_element) ¶$filename is the name of the file output.
\%tree_unit_element is the first tree unit element of the file.
This function should print the page header, in HTML,
including the <body> element.