diff --git a/docs/api.rst b/docs/api.rst
index 5404103..8cc4c0f 100644
--- a/docs/api.rst
+++ b/docs/api.rst
@@ -18,3 +18,8 @@
 .. autodata:: nvchecker.api.proxy
 .. autodata:: nvchecker.api.user_agent
 .. autodata:: nvchecker.api.tries
+
+.. py:data:: nvchecker.api.entry_waiter
+   :type: contextvars.ContextVar
+
+   This :class:`ContextVar <contextvars.ContextVar>` contains an :class:`EntryWaiter <nvchecker.api.EntryWaiter>` instance for waiting on other entries.
diff --git a/docs/requirements.txt b/docs/requirements.txt
index 3b6de1f..a68922a 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -3,3 +3,5 @@ structlog
 appdirs
 tornado>=6
 sphinx>=3.2
+# <5 has strange bottom margins for p, and no list indicators
+sphinx-rtd-theme>=0.5
diff --git a/docs/usage.rst b/docs/usage.rst
index 78a5124..417f3ba 100644
--- a/docs/usage.rst
+++ b/docs/usage.rst
@@ -746,6 +746,22 @@ container
 registry
   The container registry host. Default: ``docker.io``
 
+``registry`` and ``container`` are the host and the path used in the pull
+command. Note that the ``docker`` command allows omitting some parts of the
+container name while this plugin requires the full name. If the host part is
+omitted, use ``docker.io``, and if there is no slash in the path, prepend
+``library/`` to the path. Here are some examples:
+
++----------------------------------------------+-----------+--------------------------+
+| Pull command                                 | registry  | container                |
++==============================================+===========+==========================+
+| docker pull quay.io/prometheus/node-exporter | quay.io   | prometheus/node-exporter |
++----------------------------------------------+-----------+--------------------------+
+| docker pull nvidia/cuda                      | docker.io | nvidia/cuda              |
++----------------------------------------------+-----------+--------------------------+
+| docker pull python                           | docker.io | library/python           |
++----------------------------------------------+-----------+--------------------------+
+
 This source returns tags and supports :ref:`list options`.
 
 Check ALPM database
diff --git a/nvchecker/__main__.py b/nvchecker/__main__.py
index a98a85a..3f25ff5 100755
--- a/nvchecker/__main__.py
+++ b/nvchecker/__main__.py
@@ -13,7 +13,7 @@ from pathlib import Path
 import structlog
 
 from . import core
-from .util import VersData, RawResult, KeyManager
+from .util import VersData, RawResult, KeyManager, EntryWaiter
 from .ctxvars import proxy as ctx_proxy
 
 logger = structlog.get_logger(logger_name=__name__)
@@ -58,10 +58,12 @@ def main() -> None:
     options.httplib,
     options.http_timeout,
   )
+  entry_waiter = EntryWaiter()
   try:
     futures = dispatcher.dispatch(
       entries, task_sem, result_q,
-      keymanager, args.tries,
+      keymanager, entry_waiter,
+      args.tries,
       options.source_configs,
     )
   except ModuleNotFoundError as e:
@@ -71,7 +73,7 @@ def main() -> None:
     oldvers = core.read_verfile(options.ver_files[0])
   else:
     oldvers = {}
-  result_coro = core.process_result(oldvers, result_q)
+  result_coro = core.process_result(oldvers, result_q, entry_waiter)
   runner_coro = core.run_tasks(futures)
 
   # asyncio.run doesn't work because it always creates new eventloops
diff --git a/nvchecker/api.py b/nvchecker/api.py
index 823cdaf..e03a076 100644
--- a/nvchecker/api.py
+++ b/nvchecker/api.py
@@ -4,7 +4,8 @@
 from .httpclient import session, TemporaryError, HTTPError
 from .util import (
   Entry, BaseWorker, RawResult, VersionResult,
-  AsyncCache, KeyManager, GetVersionError,
+  AsyncCache, KeyManager, GetVersionError, EntryWaiter,
 )
 from .sortversion import sort_version_keys
-from .ctxvars import tries, proxy, user_agent, httptoken
+
+from .ctxvars import tries, proxy, user_agent, httptoken, entry_waiter
\ No newline at end of file
diff --git a/nvchecker/core.py b/nvchecker/core.py
index ae182e4..7fe9d5e 100644
--- a/nvchecker/core.py
+++ b/nvchecker/core.py
@@ -29,11 +29,12 @@ from . import slogconf
 from .util import (
   Entry, Entries, KeyManager, RawResult, Result, VersData,
   FunctionWorker, GetVersionError,
-  FileLoadError,
+  FileLoadError, EntryWaiter,
 )
 from . import __version__
 from .sortversion import sort_version_keys
 from .ctxvars import tries as ctx_tries
+from .ctxvars import entry_waiter as ctx_entry_waiter
 from . import httpclient
 
 logger = structlog.get_logger(logger_name=__name__)
@@ -219,11 +220,13 @@ class Dispatcher:
     task_sem: asyncio.Semaphore,
     result_q: Queue[RawResult],
     keymanager: KeyManager,
+    entry_waiter: EntryWaiter,
     tries: int,
     source_configs: Dict[str, Dict[str, Any]],
   ) -> List[asyncio.Future]:
     mods: Dict[str, Tuple[types.ModuleType, List]] = {}
     ctx_tries.set(tries)
+    ctx_entry_waiter.set(entry_waiter)
     root_ctx = contextvars.copy_context()
 
     for name, entry in entries.items():
@@ -311,7 +314,7 @@ def apply_list_options(
 
   return versions[-1]
 
-def _process_result(r: RawResult) -> Optional[Result]:
+def _process_result(r: RawResult) -> Union[Result, Exception]:
   version = r.version
   conf = r.conf
   name = r.name
@@ -320,11 +323,11 @@ def _process_result(r: RawResult) -> Optional[Result]:
     kw = version.kwargs
     kw['name'] = name
     logger.error(version.msg, **kw)
-    return None
+    return version
   elif isinstance(version, Exception):
     logger.error('unexpected error happened',
                   name=r.name, exc_info=r.version)
-    return None
+    return version
   elif isinstance(version, list):
     version_str = apply_list_options(version, conf)
   else:
@@ -336,10 +339,12 @@ def _process_result(r: RawResult) -> Optional[Result]:
     try:
       version_str = substitute_version(version_str, conf)
       return Result(name, version_str, conf)
-    except (ValueError, re.error):
+    except (ValueError, re.error) as e:
       logger.exception('error occurred in version substitutions', name=name)
+      return e
 
-  return None
+  else:
+    return ValueError('no version returned')
 
 def check_version_update(
   oldvers: VersData, name: str, version: str,
@@ -353,15 +358,18 @@ def check_version_update(
 async def process_result(
   oldvers: VersData,
   result_q: Queue[RawResult],
+  entry_waiter: EntryWaiter,
 ) -> VersData:
   ret = {}
   try:
     while True:
       r = await result_q.get()
       r1 = _process_result(r)
-      if r1 is None:
+      if isinstance(r1, Exception):
+        entry_waiter.set_exception(r.name, r1)
         continue
       check_version_update(oldvers, r1.name, r1.version)
+      entry_waiter.set_result(r1.name, r1.version)
       ret[r1.name] = r1.version
   except asyncio.CancelledError:
     return ret
diff --git a/nvchecker/ctxvars.py b/nvchecker/ctxvars.py
index 66a6ddc..b827850 100644
--- a/nvchecker/ctxvars.py
+++ b/nvchecker/ctxvars.py
@@ -4,13 +4,17 @@
 from __future__ import annotations
 
 from contextvars import ContextVar
-from typing import Optional
+from typing import Optional, TYPE_CHECKING
 
 from . import __version__
 
 DEFAULT_USER_AGENT = f'lilydjwg/nvchecker {__version__}'
 
+if TYPE_CHECKING:
+  from .util import EntryWaiter
+
 tries = ContextVar('tries', default=1)
 proxy: ContextVar[Optional[str]] = ContextVar('proxy', default=None)
 user_agent = ContextVar('user_agent', default=DEFAULT_USER_AGENT)
-httptoken = ContextVar('httptoken', default=None)
\ No newline at end of file
+httptoken = ContextVar('httptoken', default=None)
+entry_waiter: ContextVar[EntryWaiter] = ContextVar('entry_waiter')
\ No newline at end of file
diff --git a/nvchecker/util.py b/nvchecker/util.py
index 0181d52..0d6bb5d 100644
--- a/nvchecker/util.py
+++ b/nvchecker/util.py
@@ -66,6 +66,28 @@ class KeyManager:
     '''Get the named key (token) in the keyfile.'''
     return self.keys.get(name)
 
+class EntryWaiter:
+  def __init__(self) -> None:
+    self._waiting: Dict[str, asyncio.Future] = {}
+
+  async def wait(self, name: str) -> str:
+    '''Wait on the ``name`` entry and return its result (the version string)'''
+    fu = self._waiting.get(name)
+    if fu is None:
+      fu = asyncio.Future()
+      self._waiting[name] = fu
+    return await fu
+
+  def set_result(self, name: str, value: str) -> None:
+    fu = self._waiting.get(name)
+    if fu is not None:
+      fu.set_result(value)
+
+  def set_exception(self, name: str, e: Exception) -> None:
+    fu = self._waiting.get(name)
+    if fu is not None:
+      fu.set_exception(e)
+
 class RawResult(NamedTuple):
   '''The unprocessed result from a check.'''
   name: str
diff --git a/nvchecker_source/aur.py b/nvchecker_source/aur.py
index 6373cbe..9ff1c7a 100644
--- a/nvchecker_source/aur.py
+++ b/nvchecker_source/aur.py
@@ -58,7 +58,7 @@ class Worker(BaseWorker):
       fu = self._run_batch(batch, aur_results)
       ret.append(fu)
 
-    await asyncio.wait(ret)
+    await asyncio.gather(*ret)
 
   async def _run_batch(
     self,
diff --git a/nvchecker_source/combiner.py b/nvchecker_source/combiner.py
new file mode 100644
index 0000000..9e7dc6c
--- /dev/null
+++ b/nvchecker_source/combiner.py
@@ -0,0 +1,21 @@
+# MIT licensed
+# Copyright (c) 2021 lilydjwg <lilydjwg@gmail.com>, et al.
+
+import asyncio
+import string
+
+from nvchecker.api import entry_waiter
+
+class CombineFormat(string.Template):
+  idpattern = '[0-9]+'
+
+async def get_version(
+  name, conf, *, cache, keymanager=None
+):
+  t = CombineFormat(conf['format'])
+  from_ = conf['from']
+  waiter = entry_waiter.get()
+  entries = [waiter.wait(name) for name in from_]
+  vers = await asyncio.gather(*entries)
+  versdict = {str(i+1): v for i, v in enumerate(vers)}
+  return t.substitute(versdict)
diff --git a/nvchecker_source/container.py b/nvchecker_source/container.py
index e8bb0f3..df745b8 100644
--- a/nvchecker_source/container.py
+++ b/nvchecker_source/container.py
@@ -3,6 +3,7 @@
 
 from typing import Dict, List, NamedTuple, Optional, Tuple
 from urllib.request import parse_http_list
+from urllib.parse import urljoin
 
 from nvchecker.api import session, HTTPError
 
@@ -65,11 +66,29 @@ async def get_container_tags(info: Tuple[str, str, AuthInfo]) -> List[str]:
   res = await session.get(auth_info.realm, params=auth_params)
   token = res.json()['token']
 
-  res = await session.get(f'https://{registry_host}/v2/{image_path}/tags/list', headers={
-    'Authorization': f'Bearer {token}',
-    'Accept': 'application/json',
-  })
-  return res.json()['tags']
+  tags = []
+  url = f'https://{registry_host}/v2/{image_path}/tags/list'
+
+  while True:
+    res = await session.get(url, headers={
+      'Authorization': f'Bearer {token}',
+      'Accept': 'application/json',
+    })
+    tags += res.json()['tags']
+    link = res.headers.get('Link')
+    if link is None:
+      break
+    else:
+      url = urljoin(url, parse_next_link(link))
+
+  return tags
+
+def parse_next_link(value: str) -> str:
+  ending = '>; rel="next"'
+  if value.endswith(ending):
+    return value[1:-len(ending)]
+  else:
+    raise ValueError(value)
 
 async def get_version(name, conf, *, cache, **kwargs):
   image_path = conf.get('container', name)
diff --git a/tests/conftest.py b/tests/conftest.py
index 2f2ba4e..1b0e2e0 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -28,13 +28,14 @@ async def run(
     keymanager = core.KeyManager(None)
 
   dispatcher = core.setup_httpclient()
+  entry_waiter = core.EntryWaiter()
   futures = dispatcher.dispatch(
     entries, task_sem, result_q,
-    keymanager, 1, {},
+    keymanager, entry_waiter, 1, {},
   )
 
   oldvers: VersData = {}
-  result_coro = core.process_result(oldvers, result_q)
+  result_coro = core.process_result(oldvers, result_q, entry_waiter)
   runner_coro = core.run_tasks(futures)
 
   return await main.run(result_coro, runner_coro)
diff --git a/tests/test_anitya.py b/tests/test_anitya.py
index bdd2d46..9fd33e8 100644
--- a/tests/test_anitya.py
+++ b/tests/test_anitya.py
@@ -9,4 +9,4 @@ async def test_anitya(get_version):
   assert await get_version("shutter", {
     "source": "anitya",
     "anitya": "fedora/shutter",
-  }) == "0.95"
+  }) == "0.96"
diff --git a/tests/test_combiner.py b/tests/test_combiner.py
new file mode 100644
index 0000000..21fcbf0
--- /dev/null
+++ b/tests/test_combiner.py
@@ -0,0 +1,24 @@
+# MIT licensed
+# Copyright (c) 2021 lilydjwg <lilydjwg@gmail.com>, et al.
+
+import pytest
+pytestmark = pytest.mark.asyncio
+
+async def test_combiner(run_str_multi):
+  conf = r'''
+[entry-1]
+source = "cmd"
+cmd = "echo 1"
+
+[entry-2]
+source = "cmd"
+cmd = "echo 2"
+
+[entry-3]
+source = "combiner"
+from = ["entry-1", "entry-2", "entry-2"]
+format = "$1-$2-$3"
+'''
+
+  r = await run_str_multi(conf)
+  assert r['entry-3'] == '1-2-2'
diff --git a/tests/test_container.py b/tests/test_container.py
index fb7aedf..41efbd3 100644
--- a/tests/test_container.py
+++ b/tests/test_container.py
@@ -10,3 +10,10 @@ async def test_container(get_version):
     "container": "library/hello-world",
     "include_regex": "linux",
   }) == "linux"
+
+async def test_container_paging(get_version):
+  assert await get_version("prometheus-operator", {
+    "source": "container",
+    "registry": "quay.io",
+    "container": "prometheus-operator/prometheus-operator",
+  }) == "v0.48.1"
diff --git a/tests/test_pacman.py b/tests/test_pacman.py
index e651db5..4b1a964 100644
--- a/tests/test_pacman.py
+++ b/tests/test_pacman.py
@@ -1,11 +1,14 @@
 # MIT licensed
 # Copyright (c) 2013-2020 lilydjwg <lilydjwg@gmail.com>, et al.
 
+import pathlib
 import shutil
 import pytest
 pytestmark = [pytest.mark.asyncio,
               pytest.mark.skipif(shutil.which("pacman") is None,
-                                 reason="requires pacman command")]
+                                 reason="requires pacman command"),
+              pytest.mark.skipif(not pathlib.Path("/var/lib/pacman/sync/core.db").exists(),
+                                 reason="requires synced pacman databases")]
 
 async def test_pacman(get_version):
     assert await get_version("ipw2100-fw", {