Function            isfilename - character classification

  Syntax              boolean isfilename(int c);

  Prototype in        keyboard.h

  Remarks             determines if a character is valid for a DOS
                      filename. The following characters are NOT allowed:

                      :  ;  ,  =  +  tab  space  <  >  |  /  \  "  [  ]

  Return value        returns true if c is a valid DOS filename
                      character, FALSE otherwise.

  Note                This function checks if a character is legal for a
                      DOS filename.ext. Use ispathname() to check for a
                      valid DOS pathname character.

  See also            ispathname()