[XeTeX] : Temporarily disable Mapping=tex-text

[Sven Siegmund]

Hi,

I have selected my fonts with the optional feature Mapping=tex-text:

\setmainfont[Mapping=tex-text]{Charis SIL}

but somewhere in text I wand to temporarily disable it, e.g. when I
want to write the U+0027 APOSTROPHE which shall not be converted to
U+02BC MODIFIER LETTER APOSTROPHE. How can I do that?

I figure it can be done with \addfontfeatures{Mapping=??} but what to
write as the value of Mapping? I cannot find the default value (e.g.
the non-tex-text) in fontspec documentation. /-:

TIA,

S.