XML in a Nutshell, 3rd Edition

The version Attribute

The version attribute should have the value 1.0. Under very unusual circumstances, it may also have the value 1.1. Since specifying version="1.1" limits the document to the most recent versions of only a couple of parsers, and since all XML 1.1 parsers must also support XML 1.0, you don’t want to casually set the version to 1.1.

Don’t believe us? First answer a couple of questions:

1. Do you speak Cambodian, Burmese, Amharic, Mongolian, or Divehi?

2. Does your data contain obsolete, nontext C0 control characters such as vertical tab, form feed, or bell?

If you answered no to both of these questions, you have absolutely nothing to gain by using XML 1.1. If you answered yes to either one, then you may have cause to use XML 1.1. XML 1.0 allows Cambodian, Burmese, Amharic, etc. to be used in character data and attribute values. XML 1.1 also allows these scripts to be used in element and attribute names, which XML 1.0 does not. XML 1.1 also allows C0 control characters (except null) to be used in character data and attribute values (provided they’re escaped as numeric character references like ), which XML 1.0 does not. If either of these conditions applies to you, then you might want to use XML 1.1 (although realize you’re limiting your audience by doing so). Otherwise, you really should use XML 1.0 exclusively.