python 2 -> python 3

[Russell L. Carter]

11.1-STABLE FreeBSD 11.1-STABLE #11 r313908

Maybe I've missed it.  Are there some hints somewhere for a
person wanting to transition the default in ports to python 3?

I see in /usr/ports/Mk/bsd.default-versions.mk

**********************************

# Possible values: 9.2, 9.3, 9.4, 9.5, 9.6
PGSQL_DEFAULT?=		9.5
# Possible values: 5.6, 7.0, 7.1
PHP_DEFAULT?=		5.6
# Possible values: 2.7, 3.4, 3.5, 3.6
PYTHON_DEFAULT?=	2.7
# Possible values: 2.7
PYTHON2_DEFAULT?=	2.7
# Possible values: 3.4, 3.5, 3.6
PYTHON3_DEFAULT?=	3.6
# Possible values: 2.2, 2.3, 2.4
RUBY_DEFAULT?=		2.3

**********************************

PGSQL & RUBY options included to possibly hint at this is the
only documentation available, AFAICS.

Yet, when I set PYTHON_DEFAULT to 3.6, I get thunderbird and
firefox and chrome etc etc failing.

I only wrote my first hello world in python (3!) a few days ago, so
likely I'm a moron.

Thank you,
Russell