In v5.1.0, Tinderbox HTML export included a byte-order mark (BOM) to help browsers and other tools to recognise that the exported files are UTF-8. The BOM was dropped from v5.5.0 export, though output is still encoded as UTF-8. The BOM was dropped as so many other apps don't understand BOMs (it is a standard but one most apps' authors have chosen to actively ignore) and this caused a problem for onward use of exported data..
HTML export can export all sorts of mark-up, but for actual HTML it is advisable to add the following for thesection of the exported page's source:
<meta http-equiv="content-type" content="text/html; charset=utf-8">
This makes it even easier for ensure a web browser to figure the encoding to expect within web page it is opening.