diff --git a/docs/config.rst b/docs/config.rst
index 728bcb4fea..5c3f1bdc93 100644
--- a/docs/config.rst
+++ b/docs/config.rst
@@ -967,7 +967,4 @@ Other Rules and notes
 cli
 ===
 
-.. autoprogram:: tox.cli:cli
-   :prog: tox
-
 .. include:: links.rst
diff --git a/docs/plugins.rst b/docs/plugins.rst
index e6e714a3d3..61b045fc5a 100644
--- a/docs/plugins.rst
+++ b/docs/plugins.rst
@@ -187,22 +187,11 @@ You can and publish it like:
 Hook specifications and related API
 -----------------------------------
 
-.. automodule:: tox.hookspecs
+.. automodule:: tox.plugin.spec
     :members:
 
-.. autoclass:: tox.config.Parser()
+.. autoclass:: tox.config.sets.ConfigSet
     :members:
 
-.. autoclass:: tox.config.Config()
-    :members:
-
-.. autoclass:: tox.config.TestenvConfig()
-    :members:
-
-.. autoclass:: tox.venv.VirtualEnv()
-    :members:
-
-.. autoclass:: tox.session.Session()
-    :members:
 
 .. include:: links.rst
diff --git a/setup.cfg b/setup.cfg
index 1c36b10fd6..4625d97199 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -35,7 +35,7 @@ classifiers =
 
 [options]
 packages = find:
-python_requires = >=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*
+python_requires = >=3.5
 install_requires =
     importlib-metadata >= 0.12, <1;python_version<"3.8"
     packaging >= 14
diff --git a/src/tox/__init__.py b/src/tox/__init__.py
index e69de29bb2..dc2782c3f6 100644
--- a/src/tox/__init__.py
+++ b/src/tox/__init__.py
@@ -0,0 +1,3 @@
+from .version import __version__
+
+__all__ = ("__version__",)
diff --git a/src/tox/config/cli/for_docs.py b/src/tox/config/cli/for_docs.py
new file mode 100644
index 0000000000..95f6393fa2
--- /dev/null
+++ b/src/tox/config/cli/for_docs.py
@@ -0,0 +1,3 @@
+from .parse import _get_core_parser
+
+parser = _get_core_parser()
diff --git a/src/tox/config/cli/parse.py b/src/tox/config/cli/parse.py
index 8ecb4977e4..07fbb45407 100644
--- a/src/tox/config/cli/parse.py
+++ b/src/tox/config/cli/parse.py
@@ -22,12 +22,16 @@ def _get_base(args):
 
 
 def _get_core(args):
+    tox_parser = _get_core_parser()
+    parsed, unknown = tox_parser.parse(args)
+    handlers = {k: p for k, (_, p) in tox_parser.handlers.items()}
+    return handlers, parsed, unknown
+
+
+def _get_core_parser():
     tox_parser = ToxParser.core()
     # noinspection PyUnresolvedReferences
     from tox.plugin.manager import MANAGER
-
     MANAGER.tox_add_option(tox_parser)
     tox_parser.fix_defaults()
-    parsed, unknown = tox_parser.parse(args)
-    handlers = {k: p for k, (_, p) in tox_parser.handlers.items()}
-    return handlers, parsed, unknown
+    return tox_parser
diff --git a/src/tox/config/main.py b/src/tox/config/main.py
index 12ad121ff7..ec3fa90a80 100644
--- a/src/tox/config/main.py
+++ b/src/tox/config/main.py
@@ -38,3 +38,6 @@ def __iter__(self):
 
     def __repr__(self):
         return "{}(config_source={!r})".format(type(self).__name__, self._src)
+
+    def __contains__(self, item):
+        return item in self._envs
diff --git a/src/tox/config/sets.py b/src/tox/config/sets.py
index 21b8f079a7..e1beb1f6d5 100644
--- a/src/tox/config/sets.py
+++ b/src/tox/config/sets.py
@@ -117,6 +117,17 @@ def add_config(
         post_process=None,
         overwrite=False,
     ):
+        """
+        Add configuration.
+        
+        :param keys:
+        :param of_type:
+        :param default:
+        :param desc:
+        :param post_process:
+        :param overwrite:
+        :return:
+        """
         keys_ = self._make_keys(keys)
         for key in keys_:
             if key in self._defined and overwrite is False:
diff --git a/src/tox/config/source/ini/__init__.py b/src/tox/config/source/ini/__init__.py
index d95a4a9173..5c5369ba57 100644
--- a/src/tox/config/source/ini/__init__.py
+++ b/src/tox/config/source/ini/__init__.py
@@ -9,9 +9,8 @@
 from ..api import EnvList, Loader, Source
 from .convert import StrConvert
 from .factor import filter_for_env, find_envs
-from .replace import replace
+from .replace import BASE_TEST_ENV, replace
 
-BASE_TEST_ENV = "testenv"
 TEST_ENV_PREFIX = "{}:".format(BASE_TEST_ENV)
 
 
@@ -28,6 +27,7 @@ def __init__(self, path: Path) -> None:
             src=self,
             name=None,
             default_base=EnvList([]),
+            section_loader=self._get_section,
         )
         super().__init__(core)
         self._envs = {}  # type: Dict[str, IniLoader]
@@ -70,7 +70,9 @@ def get_section(self, item, name):
         try:
             return self._envs[item]
         except KeyError:
-            loader = IniLoader(self._get_section(item), self, name, self.BASE_ENV_LIST)
+            loader = IniLoader(
+                self._get_section(item), self, name, self.BASE_ENV_LIST, self._get_section
+            )
             self._envs[item] = loader
             return loader
 
@@ -104,13 +106,19 @@ class IniLoader(Loader, StrConvert):
     """Load from a ini section"""
 
     def __init__(
-        self, section: Optional[SectionProxy], src: Ini, name: Optional[str], default_base: EnvList
+        self,
+        section: Optional[SectionProxy],
+        src: Ini,
+        name: Optional[str],
+        default_base: EnvList,
+        section_loader,
     ) -> None:
         super().__init__(name)
         self._section = section  # type:Optional[SectionProxy]
         self._src = src  # type: Ini
         self._default_base = default_base  # type:EnvList
         self._base = []  # type:List[IniLoader]
+        self._section_loader = section_loader
 
     def __deepcopy__(self, memo):
         # python < 3.7 cannot copy config parser
@@ -127,10 +135,11 @@ def __deepcopy__(self, memo):
     def setup_with_conf(self, conf: ConfigSet):
         # noinspection PyUnusedLocal
         def load_bases(values, conf_):
-            result = []
+            result = []  # type: List[IniLoader]
             for value in values:
                 name = value.lstrip(TEST_ENV_PREFIX)
-                result.append(self._src.get_section(value, name))
+                ini_loader = self._src.get_section(value, name)  # type: IniLoader
+                result.append(ini_loader)
             return result
 
         conf.add_config(
@@ -169,11 +178,16 @@ def _load_raw_from(self, as_name, conf, key):
             raise KeyError(key)
         value = self._section[key]
         collapsed_newlines = value.replace("\\\n", "")  # collapse explicit line splits
-        replace_executed = replace(collapsed_newlines, conf, as_name)  # do replacements
+        replace_executed = replace(
+            collapsed_newlines, conf, as_name, self._section_loader
+        )  # do replacements
         factor_selected = filter_for_env(replace_executed, as_name)  # select matching factors
         # extend factors
         return factor_selected
 
+    def get_value(self, section, key):
+        return self._section_loader(section)[key]
+
     @property
     def loaders(self):
         yield self
diff --git a/src/tox/config/source/ini/replace.py b/src/tox/config/source/ini/replace.py
index ad5d849d02..07bd1bd09b 100644
--- a/src/tox/config/source/ini/replace.py
+++ b/src/tox/config/source/ini/replace.py
@@ -16,23 +16,24 @@
     """,
     re.VERBOSE,
 )
+BASE_TEST_ENV = "testenv"
 
 
-def substitute_once(val, conf, name):
+def substitute_once(val, conf, name, section_loader):
     # noinspection PyTypeChecker
-    return RE_ITEM_REF.sub(partial(_replace_match, conf, name), val)
+    return RE_ITEM_REF.sub(partial(_replace_match, conf, name, section_loader), val)
 
 
-def replace(value, conf, name):
+def replace(value, conf, name, section_loader):
     while True:  # substitution found
-        expanded = substitute_once(value, conf, name)
+        expanded = substitute_once(value, conf, name, section_loader)
         if expanded == value:
             break
         value = expanded
     return expanded
 
 
-def _replace_match(conf: Config, name, match):
+def _replace_match(conf: Config, name, section_loader, match):
     groups = match.groupdict()
     sub_type = groups["sub_type"]
     value = groups["substitution_value"]
@@ -50,10 +51,16 @@ def _replace_match(conf: Config, name, match):
         if sub_type is not None:
             key_missing_value = value
             value = sub_type
+        else:
+            value = groups["key"]
         section = groups["section"] or name
         # noinspection PyBroadException
+        if section not in conf:
+            env_conf = section_loader(section)
+        else:
+            env_conf = conf[section]
         try:
-            replace_value = conf[section][value]
+            replace_value = env_conf[value]
         except Exception:
             # noinspection PyBroadException
             try:
diff --git a/src/tox/session/cmd/list_env.py b/src/tox/session/cmd/list_env.py
index c524ad06ff..f200783ddb 100644
--- a/src/tox/session/cmd/list_env.py
+++ b/src/tox/session/cmd/list_env.py
@@ -24,7 +24,7 @@ def list_env(state: State):
 
     if not option.list_quiet and default:
         print("default environments:")
-    max_length = max(len(env) for env in (default + extra))
+    max_length = max(len(env) for env in (default.envs + extra))
 
     def report_env(name: str):
         if not option.list_quiet:
diff --git a/src/tox/session/cmd/run/single.py b/src/tox/session/cmd/run/single.py
index d90edb2c79..8e96c13444 100644
--- a/src/tox/session/cmd/run/single.py
+++ b/src/tox/session/cmd/run/single.py
@@ -13,7 +13,7 @@ def run_one(tox_env: RunToxEnv, recreate: bool, no_test: bool) -> int:
     try:
         tox_env.setup()
     except Recreate:
-        tox_env.clean(package_env=recreate)
+        tox_env.clean(package_env=False)  # restart creation once, no package please
         tox_env.setup()
 
     code = run_commands(tox_env, no_test)
diff --git a/src/tox/tox_env/package.py b/src/tox/tox_env/package.py
index 3900172331..3906e86759 100644
--- a/src/tox/tox_env/package.py
+++ b/src/tox/tox_env/package.py
@@ -1,10 +1,19 @@
 from abc import ABC, abstractmethod
 from typing import Any, List
 
+from tox.config.sets import ConfigSet
+from tox.execute.api import Execute
+from tox.tox_env.errors import Recreate
+
 from .api import ToxEnv
 
 
 class PackageToxEnv(ToxEnv, ABC):
+    def __init__(self, conf: ConfigSet, core: ConfigSet, options, executor: Execute):
+        super().__init__(conf, core, options, executor)
+        self._cleaned = False
+        self._setup_done = False
+
     def register_config(self):
         super().register_config()
 
@@ -15,3 +24,17 @@ def get_package_dependencies(self, extras=None) -> List[Any]:
     @abstractmethod
     def perform_packaging(self) -> List[Any]:
         raise NotImplementedError
+
+    def clean(self):
+        # package environments may be shared clean only once
+        if self._cleaned is False:
+            self._cleaned = True
+            super().clean()
+
+    def ensure_setup(self):
+        if self._setup_done is False:
+            try:
+                self.setup()
+            except Recreate:
+                self.clean()
+                self.setup()
diff --git a/src/tox/tox_env/python/api.py b/src/tox/tox_env/python/api.py
index ef70717bd7..4d0284b737 100644
--- a/src/tox/tox_env/python/api.py
+++ b/src/tox/tox_env/python/api.py
@@ -93,7 +93,8 @@ def cached_install(self, deps, section, of_type):
             if missing:  # no way yet to know what to uninstall here (transitive dependencies?)
                 # bail out and force recreate
                 raise Recreate()
-            new_deps = [Requirement(i) for i in (set(conf_deps) - set(old))]
+            new_deps_str = set(conf_deps) - set(old)
+            new_deps = [Requirement(i) for i in new_deps_str]
             self.install_python_packages(packages=new_deps)
 
     @abstractmethod
diff --git a/src/tox/tox_env/python/runner.py b/src/tox/tox_env/python/runner.py
index 706f718b4a..a5994eb1a5 100644
--- a/src/tox/tox_env/python/runner.py
+++ b/src/tox/tox_env/python/runner.py
@@ -3,7 +3,7 @@
 
 from packaging.requirements import Requirement
 
-from tox.tox_env.errors import Recreate, Skip
+from tox.tox_env.errors import Skip
 
 from ..runner import RunToxEnv
 from .api import NoInterpreter, Python
@@ -49,12 +49,6 @@ def setup(self) -> None:
         self.cached_install(self.conf["deps"], PythonRun.__name__, "deps")
 
         if self.package_env is not None:
-            try:
-                self.package_env.setup()
-            except Recreate:
-                self.package_env.clean()
-                self.package_env.setup()
-
             package_deps = self.package_env.get_package_dependencies(self.conf["extras"])
             self.cached_install(package_deps, PythonRun.__name__, "package_deps")
             self.install_package()
diff --git a/src/tox/tox_env/python/virtual_env/package/api.py b/src/tox/tox_env/python/virtual_env/package/api.py
index 7cf3476e89..0e7516aad0 100644
--- a/src/tox/tox_env/python/virtual_env/package/api.py
+++ b/src/tox/tox_env/python/virtual_env/package/api.py
@@ -106,8 +106,8 @@ def get_package_dependencies(self, extras=None) -> List[Requirement]:
             if key == "Requires-Dist":
                 req = Requirement(v)
                 markers = getattr(req.marker, "_markers", tuple()) or tuple()
-                for _at, (m_key, op, m_val) in enumerate(
-                    i for i in markers if isinstance(i, tuple) and len(i) == 3
+                for _at, (m_key, op, m_val) in (
+                    (j, i) for j, i in enumerate(markers) if isinstance(i, tuple) and len(i) == 3
                 ):
                     if m_key.value == "extra" and op.value == "==":
                         extra = m_val.value
@@ -117,15 +117,19 @@ def get_package_dependencies(self, extras=None) -> List[Requirement]:
                 if extra is None or extra in extras:
                     if _at is not None:
                         # noinspection PyProtectedMember
-                        del req.marker._markers[_at]
+                        del markers[_at]
+                        _at -= 1
+                        if _at > 0 and markers[_at] in ("and", "or"):
+                            del markers[_at]
                         # noinspection PyProtectedMember
-                        if len(req.marker._markers) == 0:
+                        if len(markers) == 0:
                             req.marker = None
                     result.append(req)
         return result
 
     def _ensure_meta_present(self):
         if self._distribution_meta is None:
+            self.ensure_setup()
             self.meta_folder.mkdir(exist_ok=True)
             cmd = [
                 "python",
diff --git a/src/tox/tox_env/python/virtual_env/package/artifact/api.py b/src/tox/tox_env/python/virtual_env/package/artifact/api.py
index 25459e3350..41316eac17 100644
--- a/src/tox/tox_env/python/virtual_env/package/artifact/api.py
+++ b/src/tox/tox_env/python/virtual_env/package/artifact/api.py
@@ -48,5 +48,6 @@ def _build_artifact(self) -> List[Path]:
     def perform_packaging(self) -> List[Path]:
         """build_wheel/build_sdist"""
         if self._package is None:
+            self.ensure_setup()
             self._package = self._build_artifact()
         return self._package
diff --git a/tests/unit/config/ini/replace/test_replace_tox_env.py b/tests/unit/config/ini/replace/test_replace_tox_env.py
index ee14bd47f8..e45b78308a 100644
--- a/tests/unit/config/ini/replace/test_replace_tox_env.py
+++ b/tests/unit/config/ini/replace/test_replace_tox_env.py
@@ -54,3 +54,11 @@ def test_replace_within_tox_env_missing_default_env_only(example):
     env_config.add_config(keys="o", of_type=str, default="o", desc="o")
     result = env_config["o"]
     assert result == "one"
+
+
+def test_replace_within_tox_env_from_base(example):
+    env_config = example("p = one\n[testenv:a]\no = {[testenv]p}")
+    env_config.add_config(keys="p", of_type=str, default="p", desc="p")
+    env_config.add_config(keys="o", of_type=str, default="o", desc="o")
+    result = env_config["o"]
+    assert result == "one"
diff --git a/tox.ini b/tox.ini
index cc5cb76f8b..377645e11f 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,10 +1,9 @@
 [tox]
 envlist =
     py38
-    py37
     py35
+    py37
     py36
-    pypy3
     coverage
     fix_lint
     docs
@@ -16,7 +15,7 @@ requires =
     virtualenv >= 10
 
 [testenv]
-description = run the tests with pytest under {basepython}
+description = run the tests with pytest
 setenv = COVERAGE_FILE = {env:COVERAGE_FILE:{toxworkdir}/.coverage.{envname}}
          VIRTUALENV_NO_DOWNLOAD = 1
 passenv = http_proxy https_proxy no_proxy SSL_CERT_FILE PYTEST_*
@@ -40,7 +39,7 @@ description = invoke sphinx-build to build the HTML docs
 basepython = python3.7
 extras = docs
 commands = sphinx-build -d "{toxworkdir}/docs_doctree" docs "{toxworkdir}/docs_out" --color -W -bhtml {posargs}
-           python -c 'import pathlib; print("documentation available under file://\{0\}".format(pathlib.Path(r"{toxworkdir}") / "docs_out" / "index.html"))'
+           python -c 'import pathlib; print("documentation available under file://{0}".format(pathlib.Path(r"{toxworkdir}") / "docs_out" / "index.html"))'
 
 [testenv:package_description]
 description = check that the long description is valid
@@ -49,7 +48,7 @@ deps = twine >= 1.12.1
        # TODO installing readme-renderer[md] should not be necessary
        readme-renderer[md] >= 24.0
        pip >= 18.0.0
-skip_install = true
+package = skip
 extras =
 commands = pip wheel -w {envtmpdir}/build --no-deps .
            twine check {envtmpdir}/build/*
@@ -64,7 +63,7 @@ passenv = {[testenv]passenv}
 extras = lint
 deps =
     pre-commit >= 1.14.4, < 2
-skip_install = True
+package = skip
 commands = pre-commit run --all-files --show-diff-on-failure {posargs}
            python -c 'import pathlib; print("hint: run {} install to add checks as pre-commit hook".format(pathlib.Path(r"{envdir}") / "bin" / "pre-commit"))'
 
@@ -75,7 +74,7 @@ description = [run locally after tests]: combine coverage data and create report
 deps = {[testenv]deps}
        coverage >= 4.4.1, < 5
        diff_cover
-skip_install = True
+package = skip
 passenv = {[testenv]passenv}
           DIFF_AGAINST
 setenv = COVERAGE_FILE={toxworkdir}/.coverage
@@ -92,7 +91,7 @@ parallel_show_output = True
 # PYTHONPATH=.:$PYTHONPATH python3 -m tox -e exit_code
 basepython = python3.7
 description = commands with several exit codes
-skip_install = True
+package = skip
 commands = python3.7 -c "import sys; sys.exit(139)"
 
 [testenv:X]
@@ -160,7 +159,7 @@ commands = python {toxinidir}/tasks/release.py --version {posargs}
 [testenv:notify]
 description = notify people about the release of the library
 basepython = python3.7
-skip_install = true
+package = skip
 passenv = *
 deps = gitpython >= 2.1.10
        packaging  >= 17.1