Needed text attributes for body:value and TextQuoteSelector

[gautierchomel]

Previous discussion #16 was too large to be addressed correctly. "Rich Text" is a too large concept. Instead, I propose to list the attributes which are necessary for a correct reading experience.

For now we identified language of parts (See #19 and #20) as an accessibility need.

[gautierchomel]

Maybe the issue is that we are using TextQuoteSelector for both identifying a target and to populate a citation export.