Success Criterion 3.1.2 (Language of Parts) states that the changes in language should be marked using language attributes to qualify for AA conformance.
This example should test the usage of lang and xml:lang attributes on a normal element that are well-formed, but not likely valid. HTML_CodeSniffer cannot vouch for the validity of otherwise well-formed tags. For instance, the "en-AUS" example below is well-formed because the "en" can be followed by a two-character country, three-character "extlang", or four-character script subtag - therefore it will parse as language and extlang. It is likely not what the author intended, which is likely "en-AU", and would not be valid if it was compared against the IANA language register.
(The "*" represents either "Lang" or "XmlLang" depending on which attribute applies.)