def to_s_append( ds, s )
      s << '$' << name.to_s
      s << ':' << sql_field.to_s if sql_field
      s << '/*' << small_source  << '*/'
    end
def to_s_append( ds, s )
      s << '$' << name.to_s
      s << ':' << sql_field.to_s if sql_field
      s << '/*' << small_source  << '*/'
    end
this is inserted into the generated SQL from a dataset that
 contains PlaceHolder instances.