Comment by zahlman

I mean, yes, the standard says that parsing should be case sensitive (I also found https://stackoverflow.com/questions/7414747). But people parse it as if it were case insensitive all the time, in part thanks to tradition established by HTML. In this case, the XML looked like

  <MESSAGES>
    <INFO path="src/main/Kotlin/Example.kt" line="1" column="1">
      This is a message from the compiler about a line of code.
    </INFO>
  </MESSAGES>

and other code would try to filter the messages for presentation. And it appears that even if their spec demanded uppercase tag names, they were case-folding them for lookup purposes (to map "INFO" to some constant like CompilerMessageSeverity.INFO, or something like that).