The CRM module has the first encounter with this that I've seen. It's in crm/crm_phonecall.py at the very top. Appears to be new to 7.0. What does this mean? I can't find any good explanation in the documentation (the search feature was taken away!). Code sample from crm_phonecall.py:

from openerp.addons.base_status.base_state import base_state
# [...]

class crm_phonecall(base_state, osv.osv):
    """ Model for CRM phonecalls """
    _name = "crm.phonecall"
    _description = "Phonecall"
    _order = "id desc"
    _inherit = ['mail.thread']
    _columns = {
        # base_state required fields
        'date_action_last': fields.datetime('Last Action', readonly=1),
        'date_action_next': fields.datetime('Next Action', readonly=1),
        'create_date': fields.datetime('Creation Date' , readonly=True),
            # [...]

Going to that module there is a very small description:

""" Base utility mixin class for objects willing to manage their state.
    Object subclassing this class should define the following colums:
    - ``date_open`` (datetime field)
    - ``date_closed`` (datetime field)
    - ``user_id`` (many2one to res.users)
    - ``partner_id`` (many2one to res.partner)
    - ``email_from`` (char field)
    - ``state`` (selection field)
"""

But this isn't explaining all that much. Anyone have any clearer explanation?

Any help would be appreciated!