trytond documentation: missing _parent behaviour
It can be used in fields.depends and in PYSON statements. Did I miss other?
Should it be added to different sections of the docs?
eg.
PYSON: http://trytond.readthedocs.io/en/latest/topics/pyson.html
fields: http://trytond.readthedocs.io/en/latest/ref/models/fields.html