When inserting the following XML Structure, IntelliJ assumes it is not well formed, although it is by the xml specification, and also when validating, the parser doesn't find any error: <root> <:elem>blah</:elem> </root> the problem seems to be the colon as first character in the element name without any namespace bound. Although it's weird it's allowed (see xml spec paragraph 2.3 and xerces implementation) intellijs parser should not throw errors.