Special case - rotated Portrait headers on Landscape pages
$mpdf->forcePortraitHeaders = true;
In v2.3 this was updated to work for non-HTML headers/footers as well.
This is a quick fix which rotates HTML headers and Footers on landscape pages in the following conditions:
document orientation is portrait
when adding a page, you must only call $mpdf->AddPage(‘L’) or <pagebreak orientaion=”landscape” /> - if you try to set new margins/headers etc. for new landscape pages when forcePortrait=true, it will go wrong