There are times you may wonder which application handles a certain file extension.
In Windows there are really two concepts: File Extension and File Type. File extension can be associated to a file type. Applications work on file type, not directly on file extension.
You can use assoc to find out which file type a file extension is associated with, and ftype to find out which application is registered to handle the file type.
D:\>ftype htmlfilehtmlfile="D:\Program Files\Internet Explorer\IEXPLORE.EXE" -nohome