What is "Office XML Handler"?

Question

What is "Office XML Handler"? It seems to be a program from MS Office that likes to be unhelpfully associated with various file formats on Windows. Here's what has been happening when I double-click ".log" files and it opens with Office XML Handler:

Of course I can fix this by right-clicking and changing the program it opens with.

But what is Office XML Handler? Are there any file types that it should be associated with?

Answer 1

"Office XML Handler" is the display name of the process MSOXMLED.EXE, which is locaded in C:\Program Files (x86)\Common Files\Microsoft Shared\OFFICE15 on my computer. It is used to open XML files (perhaps also other extentions?) and detect which MS Office program the file should be associated with (if any), and then open the file with that program.

This is explained in https://stackoverflow.com/a/1569619/1858923:

So when an XML file is double-clicked in Explorer, Windows will launch MSOXMLED.EXE. This application is now looking inside the XML file and searches for an XML processing instruction. This processing instruction named mso-application can specify a ProgId:

<?mso-application progid="Word.Document"?>

...

So finally MSOXMLED.EXE will start the appropriate Office application or launch the default XML application which is specified under

HKEY_CLASSES_ROOT\XEV.GenericApp\shell\open\command

Clearly I got the error message because the file it was trying to open did not have an mso-application tag that would tell MSOXMLED.EXE how to open the file, and I don't have the key HKEY_CLASSES_ROOT\XEV.GenericApp\shell\open\command set, so it doesn't know what to do with the file.