Generative environments, and disable lxml on pypy3 which doesn't work yet.

tox.ini

@@ -1,5 +1,6 @@
 [tox]
-envlist = py26, py27, pypy, pypy3, py34, docs, style
+envlist = py{26,27,34,py,py3}, docs, style
+
 
 [testenv]
 # by default tox runs with --pre which tickles this bug:
@@ -8,39 +9,21 @@ install_command = pip install {opts} {packages}
 commands =
     py.test [] jsonschema
     {envpython} -m doctest README.rst
-deps =
-    {[testenv:notpy34]deps}
-    {[testenv:py34]deps}
-
-[testenv:py26]
-deps =
-    {[testenv:notpy34]deps}
-    {[testenv:all]deps}
-    argparse
-    unittest2
-
-[testenv:py34]
-commands =
-    py.test [] jsonschema
-    {envpython} -m doctest README.rst
-deps =
-    {[testenv:all]deps}
-    {[testenv:notpy26]deps}
-
-[testenv:notpy34]
-deps =
-    mock
-
-[testenv:notpy26]
-deps =
-    rfc3987
-
-[testenv:all]
+    py{26,27,34,py}: sphinx-build -b doctest docs {envtmpdir}/html
 deps =
     pytest
-    sphinx
     strict-rfc3339
     webcolors
+    py{27,34,py,py3}: rfc3987
+
+    py26: argparse
+    py26: unittest2
+    py{26,27,py,py3}: mock
+
+    py{26,27,34}: lxml
+    pypy: git+https://github.com/amauryfa/lxml.git@cffi
+    py{26,27,34,py}: sphinx
+
 
 [testenv:coverage]
 commands =
@@ -48,10 +31,9 @@ commands =
     coverage report --show-missing
     coverage html
 deps =
-    {[testenv:notpy34]deps}
-    {[testenv:py34]deps}
     coverage
 
+
 [testenv:docs]
 basepython = python
 changedir = docs
@@ -60,13 +42,16 @@ deps =
 commands =
     sphinx-build [] -W -b html -d {envtmpdir}/doctrees . {envtmpdir}/html
 
+
 [testenv:style]
 deps = flake8
 commands =
     flake8 [] --max-complexity 10 jsonschema
 
+
 [flake8]
 ignore = E203,E302,E303,E701,F811
 
+
 [pytest]
 addopts = -r s -s