XML file encoding format “utf-8” VS “UTF-8”?

Question

When the XML file was convert to ASCII. It is different values for user at the three characters of utf and UTF.

Answer 1

From the XML specification:

"XML processors SHOULD match character encoding names in a case-insensitive way"

This indicates that you can use upper case or lower case or even mixed case if you wish. However, the specification uses "UTF-8" in all its examples so for consistency I'd go with that.