Mask:AddBlock(R,C,ShortName,VarName,Block,DoGet,Pict,When,Valid):
  public: return true
  This object is appended with the next column (variable) defined by
  the code block.

  Parameter description:
  ~~~~~~~~~~~~~~~~~~~~~~
  R: numeric: no default
   Position of edited data (row) relative to left upper window corner.

  C: numeric: no default
   Position of edited data (column) relative to left upper window corner.

  ShortName: character: default is ""
   The column name used in Browse mode.

  VarName: character: default je ShortName
   Edited variable name, or the database field name saved as information
   to clipper Get object, created in this method and saved to DoGet array.
   The clipper get object should know the edited variable name.

  Block: code_block:  no default
   The code block of get/set type, can be created by clipper functions
   FieldBlock(), FieldWBlock(), MemVarBlock() or by your own piece
   of code.

  DoGet: code_block: default is the virtual_method_Browse:DoGet()
   The code block which by the help of the Get object edits the variable
   (database field), of the respective table column. For properly use,
   you can study source code of method DBrowse:DoGet in file c_DBrowse.prg,
   and static function SetUsers in c_Menu.prg.

  Picture: character: default is ""
   The display mask for the column display mode.

  When: code_block: default is {||true}
   The code block evaluated before the begining of the editation of this
   column, if returns false no editation is processed. It enables to produce
   the computed table columns or the read-only columns.

  Valid: code_block: default is {||true}
   The code block evaluated after finishing of the current column editation
   for its validation. (if returns true the new value is valid)