This is more a sort of curiosity. While working on a multilingual web application I noticed that certain characters like punctuation marks (!?.;,) at the end of a block element are rendered as if they were placed at the beginning instead when the writing direction is right-to-left (as it is the case for certain Asian languages I do not speak).
In other words, The string
Hello, World!
is rendered as
!Hello, World
when placed in a div block with direction: rtl
This becomes even more evident if the text is split in two parts and given different colors: a contiguous chunk of text at the end is rendered in two separated regions:
What's the point of this behavior? I guess this must be a peculiarity of (all?) right-to-left languages which is automatically handled by the browser, so I don't need to care about it, or should I?
The reason is that the exclamation mark “!” has the BiDi class O.N. ('Other Neutrals'), which means effectively that it adapts to the directionality of the surrounding text. In the example case, it is therefore placed to the left of the text before it. This is quite correct for languages written right to left: the terminating punctuation mark appears at the end, i.e. on the left.
Normally, you use the CSS code direction: rtl or, preferably, the HTML attribute dir=rtl for texts in a language that is written right to left, and only for them. For them, this behavior is a solution, not a problem.
If you instead use direction: rtl or dir=rtl just for special effects, like making table columns laid out right to left, then you need to consider the implications. For example, in the table case, you would need to set direction to ltr for each cell of the table (unless you want them to be rendered as primarily right to left text).
If you have, say, an English sentence quoted inside a block of Arabic text, then you need to set the directionality of an element containing the English text to ltr, e.g.
<blockquote dir=ltr>Hello, World!</blockquote>
A similar case (just with Arabic inside English text) is discussed as use case 6 in the W3C document What you need to know about the bidi algorithm and inline markup (which has a few oddities, though, like using cite markup for quoted text, against W3C recommendations).