I've seen in several articles on the Wiki, some differences about how this is done, and I'm confused about the differences: 

Font_Switching says: "There is a font switch \em to emphasize text. This is somewhat special: it does automatic italic correction and changes the alternative depending on the current alternative. For example, if the current font alternative is normal (i.e. upright), \em switches to slanted; and if the current font alternative is slanted, \em switches to normal." And using \definebodyfontenvironment[default][em=italic] to use italic instead of slanted; for OpenType fonts, recommends using \definefontfeature[default][default][itlc=yes] to also activate the italic correction. However, this seems not to work in x(ht)ml export.

If you go to Export, it says: "Also note that switches like \em don’t translate into output structure, you need to \definehighlight[emph][style={\em}] and use as \emph{emphasized}." This is what I'm currently using. Other parts of the Wiki show a similar solution, but using style=italic, or style={\it}; I've seen others, but now I can't find them. 

Could you please guide me as to where is this documented in the manuals? Is there any particular reason to choose any of these approaches above the others? What is the recommended option if you want to have the \em properties for emphasized text, but works for BOTH pdf and x(h)tml export?

Thank you for your time.

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