The <bdo> element defines bi-directional override, which is used to override the current text direction. This is intended for languages (eg: Persian, Hebrew) which read right to left.
HTML file:
Displayed by browser:
<p>If your browser supports bi-directional override (bdo), the next line will be written from right to left (rtl) -- </p>
<bdo dir="rtl">This text will be written from right to left</bdo>
If your browser supports bi-directional override (bdo), the next line will be written from right to left (rtl) --
This text will be written from right to left
I tried reading this in the mirror -- the individual letters are not backwards, so it cannot be read! So, in english, it's pretty useless for playing a prank on someone...