2.2.25 [HTML5:2014] Section 4.10.5.1.14 File Upload state (type=file)

C0040: The accept attribute is used to filter the file selection from the file picker

The specification states:

 ... File Upload state (type=file)
     ...
     User agents may use the value of this attribute to display a more appropriate user 
     interface than a generic file picker. ...

IE11 Mode, IE10 Mode, IE9 Mode, and EdgeHTML Mode (All versions)

The accept attribute is used to filter the file selection from the file picker.