Everything you need to know about XML 1.1 can be summed up in two rules.
Don't use it.
(For experts only) If you speak Mongolian, Yi, Cambodian, Amharic, Dhivehi, Burmese, or a very few other languages and you want to write your markup (not your text but your markup) in these languages, you can set the version attribute of the XML declaration to 1.1. Otherwise, refer to rule 1.
XML 1.1 does several things, one of them marginally useful to a few developers, the rest actively harmful.
It expands the set of characters allowed as name characters.
The C0 control characters (except for NUL) such as form feed, vertical tab, BEL, and DC1 through DC4 are now allowed in XML text provided they are escaped as character references. ...