- Available for Impleicit and Explicit,

  - Does not filter names with leading underscore,

  - Accepts optional 'filter' and 'extra' arguments.  If 'filter'
    is provided, then it must be a callable object and it is
    called with four arguments:

      inst -- The object in which an attribute is found

      name -- The attribute name

      v -- The attribute value

      extra -- The 'extra' value passed to 'acquire' or None.

    The filter function should return 1 if the attribute should
    be returned by acquire and 0 otherwise.  It may also raise an
    error, in which case the error is propigated.