Having tried epub3, html, tei, db5, epub, icml, muse, rst and textile I am getting at best something like this
<del>ou <bold>cest</bold> par cette force, <bold>que</bold> la planette</del>
while I need
<del>ou </del><bold+del>cest</bold+del><del> par cette force, </del><bold+del>que</bold+del><del> la planette</del>
The result will be stored in Filemaker Pro and converted by calculation to Adobe Tagged Text.
Icml comes close, but treats underlined text as normal text, a bug surely.
Hopeless quest?