Note that this reference documentation is identical to the help that is displayed in MATLAB when you type “help appendstruct”.

  APPENDSTRUCT appends a structure to a structure or struct-array.
  It also works if the initial structure is an empty structure or
  an empty double array. It also works if the input structures have 
  different fields.
 
  Use as
    ab = appendstruct(a, b)
 
  See also PRINTSTRUCT, COPYFIELDS, KEEPFIELDS, REMOVEFIELDS