double.sided — Is the document to be printed double sided?
This parameter is useful when printing a document on both sides of the paper.
if set to non-zero, documents are formatted using different page-masters for odd and even pages. These can differ by using a slightly wider margin on the binding edge of the page, and alternating left-right positions of header or footer elements.
If set to zero (the default), then only the 'odd' page masters are used for both even and odd numbered pages.
See also force.blank.pages,
page.margin.inner and
page.margin.outer.