When you have a text, you write either in a right to left direction, like in Arab or Hebrew, or you write in a left to right direction, like in English or Russian. In OmegaWiki, we are going to support the orientation for right to left once Multilingual MediaWiki is integrated in our software.
I have given SignWriting a lot of thought lately. This is a script that goes top to bottom. What I just realised is, that as as consequence a left to right word mixed into such an environment would also go top to bottom. It makes however as much sense to have a right to left word also go in the same direction.
The problem is that when you have both RTL and LTR in a top down environment, it will seem odd.