Mask:AddField(R,C,ShortName,Field,Picture,When,Valid):
  public: return true
  The object is appended with the column defined as normal database field.

  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.

  cField: character: no default
   The full name of the memo field (field->name), if there is no prefix
   it is accepted from instvar variable View:Alias.

  cPicture: 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)

  nRowSize: numeric: default is MaxRow()/3
   MemoEdit window height in number of rows.

  nColSize: numeric: default is MaxCol()/2
   MemoEdit window width in number of columns.