This reverses the text that is embedded in it. Used when dealing with other languages that write from right to left. For example Arabic.
<bdo dir="rtl">This text will be backwards.</bdo>
This will return the text backwards. e.g. (.sdrawkcab eb lliw txet sihT)
Either choose "ltr" for left to right or "rtl" for right to left. This declares what direction the text goes.
A link to a page with more info, then the name of the site the info came from (i.e. W3Schools).