Richard Gillam’s handy book, Unicode Demystified: A Practical Programmers Guide to the Encoding Standard, contains an example of right-to-left text appearing in a prevailing left-to-right writing direction:
Avram said “מזל טוב.” and smiled.
Whether you see here what you are meant to see here will depend on your browser's Unicode support, and whether you have Hebrew fonts installed. Properly rendered, it will look something like this:
In reading order, the first character after “said” is the “מ” character to the left of the closing quotation mark. The text then runs from right to left until the full-stop, and then resumes with “and smiled”. In Unicode, this text is not represented in rendering order, but reading order – it is up to the renderer to make space and reverse direction at the correct points. Here is the text represented as XML in a paragraph in an ODF document (get the document here):
<text:p>Avram said “מזל טוב.‏” and smiled.</text:p>
One of the great things about XML is its solid basis in Unicode and therefore its use of the Universal Character Set (ISO/IEC 10646). XML defines a number of encodings for this character set, and in the XML above the numeric character reference mechanism is used for the Hebrew characters. Notice, just to the left of the full stop the use of U+200F 'RIGHT-TO-LEFT MARK' which specifies that the full stop is part of the right-to-left character sequence.
Viewing this document in three ODF applications (OpenOffice 3, Google Docs with FireFox, and the new MS Office 2007 SP2) give the correct result every time. That is good news.
And if, for an ODF application, the character sequence did not appear correctly (if, say, the full stop was out-of-place) we would be able to say unequivocally that it was faulty; and we would be able to point to the Unicode specification where the correct behaviour was described. We (the user) would be able to bang the table and demand the bug was fixed.
This kind of process is one one of the pillars of conformance testing: application conformance testing, to be exact. Where we have a solid spec and observable behaviour we can compare the two and make a judgement.
Where we don't have a solid spec, things get trickier. For the standardiser's viewpoint, and if its not too highfalutin (and anyway, I claim Cambridge resident's special rights), we might want to quote Wittgenstein on such occasions: "Whereof one cannot speak, thereof one must be silent".