Does

‮ 0123456789 ‬ 0123456789

display as

9876543210 0123456789 ???

Let's see:

‮ 0123456789 ‬ 0123456789

Not exactly... In Chrome and Firefox on Linux, Chrome, Firefox, & Safari on OS X; and Chrome and Firefox on Windows, it comes out as

0123456789 9876543210

... which is weird.

In IE 8 on Windows 7, it comes out as

98765432100123456789

...which seems to be correct except for the treatment of the space in between the two numerical strings. (Or maybe that's correct as well -- space is a "weak" character, like punctuation, and so maybe the Unicode Rules imply that all the spaces end up at the edges?)

Anyhow, apparently Black Hat Guy has managed to warp the implementation of bidirectional text overrides in all non-Microsoft browser projects, so that the effect of his interventions is non-deterministic in the absence of detailed knowledge about his collaborators' browser and OS choices.