If Command Extensions are enabled, external command invocation through the command line or the START command changes as follows: ...

If Command Extensions are enabled, external command invocation through the command line or the START command changes as follows:  non-executable files may be invoked through their file association just     by typing the name of the file as a command.  (e.g.  WORD.DOC would     launch the application associated with the .DOC file extension).     See the ASSOC and FTYPE commands for how to create these     associations from within a command script.  When executing an application that is a 32-bit GUI application, CMD.EXE     does not wait for the application to terminate before returning to     the command prompt.  This new behavior does NOT occur if executing     within a command script.  When executing a command line whose first token is the string "CMD "     without an extension or path qualifier, then "CMD" is replaced with     the value of the COMSPEC variable.  This prevents picking up CMD.EXE     from the current directory.  When executing a command line whose first token does NOT contain an     extension, then CMD.EXE uses the value of the PATHEXT     environment variable to determine which extensions to look for     and in what order.  The default value for the PATHEXT variable     is:          .COM;.EXE;.BAT;.CMD      Notice the syntax is the same as the PATH variable, with     semicolons separating the different elements.  When searching for an executable, if there is no match on any extension, then looks to see if the name matches a directory name.  If it does, the START command launches the Explorer on that path.  If done from the command line, it is the equivalent to doing a CD /D to that path.