Mixing R-L and L-R scripts (as has been discussed here on many occasions) is a ripe arena for mysterious behavior. Given that even monolingual texts in R-L scripts will often include L-R characters, it can get hairy quickly. A desire to try to avoid having visible markers in text around the transitions is partly why the Unicode spec around bidi text is so complicated.

> A desire to try to avoid having visible markers in text around the transitions is partly why the Unicode spec around bidi text is so complicated.

Yeah but at least we can read ancient boustrophedon-style texts in plaintext, the way they were meant to be read, free of 21st century anachronisms like indication of directionality.

Unfortunately, we're still waiting for Unicode to cover Rongorongo, which has lines of alternating orientation for two readers sitting opposite one another to take turns reading it line by line.