.pg
.x union
.x map
.x end
.lt
------------------------------------------------------------------------
UNION
  MAP
    ...
  END
  .
   .
    .
  MAP
    ...
  END
END
------------------------------------------------------------------------
.el
.b 3
These macros will generate the appropriate location counter assignements inside
the structure to overlay memory locations.  Each set of allocation directives
between the MAP and END macros will be based on the same starting memory
location, i.e. at the location defined by the UNION macro. 
.b
For every UNION and MAP macro, there must be a corresponding END macro.
.b
These macros can only be used inside a STRUCT macro.
.b
For example:
.b
.lt
	struct	uic
	  ...
	  union
	    map
		uic.member: 	.blkw 1
		uic.group: 	.blkw 1
	    end
	    map
		uic.longword: 	.blkl 1
	    end
	  end
	  ...
	end
.el
.b
See also STRUCT.