[O] How to add custom markup elements and to define custom backends?

[Vladimir Lomov]

Hello,
sometimes I need markup elements than missing in Org mode, for example
combination of both bold and italic. Some backends, for instance html
and latex (with minor exception) support such combinations. So I wonder
1) how to define custom or new markup elements that can be used in
   backends, if it is possible
2) and how to extend or customize (write a custom backend) to take into
   accout these new elements.

Thanks in advance, Vladimir Lomov

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