@documentdescription: Summary Text
When producing HTML output for a document, makeinfo writes a
<meta> element in the <head> to give some idea of the
content of the document. By default, this description is the title
of the document, taken from the @settitle command
(see settitle). To change this, use the @documentdescription
environment, as in:
@documentdescription
descriptive text.
@end documentdescription
This will produce the following output in the <head> of the HTML:
<meta name=description content="descriptive text.">
@documentdescription must be specified before the first node of
the document.