prompt: We are currently solving the following issue within our repository. Here is the issue text:
  --- BEGIN ISSUE ---
  Options of `point` argument
  Documentation of `point` argument in marks isn't very easily discoverable.
  
  Recently I tried to create a chart with colored line and points. My first try was with `mark_line(color="red", point=True)`, similarly to [this example](https://altair-viz.github.io/gallery/line_chart_with_points.html), but it produced red line with blue points. This turned out to be current default behavior of Vega-lite (found in [this issue](https://github.com/vega/vega-lite/issues/6111)).
  
  After some digging, I found that `point` can be "an object defining the properties of the overlayed points." (which seems to imply `OverlayMarkDef`, but simple dictionary showed to be enough). I think it would be really helpful to have this slightly easier to find. A "Line chart with points" example seems like a good place.
  
  So, what do you think about adding some sort of variation of the following code snippet in that example?
  ```python
  import altair as alt
  import numpy as np
  import pandas as pd
  
  x = np.arange(100)
  source = pd.DataFrame({"x": x, "f(x)": np.sin(x / 5)})
  
  # Only this part will be added
  alt.Chart(source).mark_line(
      color="red", point={"color": "red"}
  ).encode(
      x="x",
      y="f(x)"
  )
  ```
  ![issue_altair_point-argument_example](https://user-images.githubusercontent.com/24854248/79694414-c5890880-8278-11ea-884b-ab9d4969b717.png)
  
  If this is OK, I would like to help with PR. Thanks.
  
  --- END ISSUE ---
  
  Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
  --- BEGIN FILES ---
  Path: `altair/examples/line_chart_with_points.py`
  Content:
  ```
  1 """
  2 Line Chart with Points
  3 ----------------------
  4 This chart shows a simple line chart with points marking each value.
  5 """
  6 # category: line charts
  7 import altair as alt
  8 import numpy as np
  9 import pandas as pd
  10 
  11 x = np.arange(100)
  12 source = pd.DataFrame({
  13   'x': x,
  14   'f(x)': np.sin(x / 5)
  15 })
  16 
  17 alt.Chart(source).mark_line(point=True).encode(
  18     x='x',
  19     y='f(x)'
  20 )
  21
  ```
  --- END FILES ---
  
  Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.
  
  Here is an example:
  
  ```diff
  diff --git a/examples/server_async.py b/examples/server_async.py
  --- a/examples/server_async.py
  +++ b/examples/server_async.py
  @@ -313,4 +313,4 @@
   
   
   if __name__ == "__main__":
  -    asyncio.run(run_async_server("."), debug=True)
  +    asyncio.run(run_async_server(), debug=True)
  diff --git a/examples/server_sync.py b/examples/server_sync.py
  --- a/examples/server_sync.py
  +++ b/examples/server_sync.py
  @@ -313,5 +313,5 @@
   
   
   if __name__ == "__main__":
  -    server = run_sync_server(".")
  +    server = run_sync_server()
       server.shutdown()
  
  ```
  
golden_diff: diff --git a/altair/examples/line_chart_with_points.py b/altair/examples/line_chart_with_points.py
  --- a/altair/examples/line_chart_with_points.py
  +++ b/altair/examples/line_chart_with_points.py
  @@ -1,7 +1,9 @@
   """
   Line Chart with Points
   ----------------------
  -This chart shows a simple line chart with points marking each value.
  +This chart shows a simple line chart with points marking each value. Use
  +``point=True`` for points with default appearance or customize it with
  +``OverlayMarkDef()``.
   """
   # category: line charts
   import altair as alt
  @@ -14,7 +16,9 @@
     'f(x)': np.sin(x / 5)
   })
   
  -alt.Chart(source).mark_line(point=True).encode(
  +alt.Chart(source).mark_line(
  +    point=alt.OverlayMarkDef(color="red")
  +).encode(
       x='x',
       y='f(x)'
   )
  
verification_info: {"golden_diff": "diff --git a/altair/examples/line_chart_with_points.py b/altair/examples/line_chart_with_points.py\n--- a/altair/examples/line_chart_with_points.py\n+++ b/altair/examples/line_chart_with_points.py\n@@ -1,7 +1,9 @@\n \"\"\"\n Line Chart with Points\n ----------------------\n-This chart shows a simple line chart with points marking each value.\n+This chart shows a simple line chart with points marking each value. Use\n+``point=True`` for points with default appearance or customize it with\n+``OverlayMarkDef()``.\n \"\"\"\n # category: line charts\n import altair as alt\n@@ -14,7 +16,9 @@\n   'f(x)': np.sin(x / 5)\n })\n \n-alt.Chart(source).mark_line(point=True).encode(\n+alt.Chart(source).mark_line(\n+    point=alt.OverlayMarkDef(color=\"red\")\n+).encode(\n     x='x',\n     y='f(x)'\n )\n", "issue": "Options of `point` argument\nDocumentation of `point` argument in marks isn't very easily discoverable.\r\n\r\nRecently I tried to create a chart with colored line and points. My first try was with `mark_line(color=\"red\", point=True)`, similarly to [this example](https://altair-viz.github.io/gallery/line_chart_with_points.html), but it produced red line with blue points. This turned out to be current default behavior of Vega-lite (found in [this issue](https://github.com/vega/vega-lite/issues/6111)).\r\n\r\nAfter some digging, I found that `point` can be \"an object defining the properties of the overlayed points.\" (which seems to imply `OverlayMarkDef`, but simple dictionary showed to be enough). I think it would be really helpful to have this slightly easier to find. A \"Line chart with points\" example seems like a good place.\r\n\r\nSo, what do you think about adding some sort of variation of the following code snippet in that example?\r\n```python\r\nimport altair as alt\r\nimport numpy as np\r\nimport pandas as pd\r\n\r\nx = np.arange(100)\r\nsource = pd.DataFrame({\"x\": x, \"f(x)\": np.sin(x / 5)})\r\n\r\n# Only this part will be added\r\nalt.Chart(source).mark_line(\r\n    color=\"red\", point={\"color\": \"red\"}\r\n).encode(\r\n    x=\"x\",\r\n    y=\"f(x)\"\r\n)\r\n```\r\n![issue_altair_point-argument_example](https://user-images.githubusercontent.com/24854248/79694414-c5890880-8278-11ea-884b-ab9d4969b717.png)\r\n\r\nIf this is OK, I would like to help with PR. Thanks.\n", "before_files": [{"content": "\"\"\"\nLine Chart with Points\n----------------------\nThis chart shows a simple line chart with points marking each value.\n\"\"\"\n# category: line charts\nimport altair as alt\nimport numpy as np\nimport pandas as pd\n\nx = np.arange(100)\nsource = pd.DataFrame({\n  'x': x,\n  'f(x)': np.sin(x / 5)\n})\n\nalt.Chart(source).mark_line(point=True).encode(\n    x='x',\n    y='f(x)'\n)\n", "path": "altair/examples/line_chart_with_points.py"}], "after_files": [{"content": "\"\"\"\nLine Chart with Points\n----------------------\nThis chart shows a simple line chart with points marking each value. Use\n``point=True`` for points with default appearance or customize it with\n``OverlayMarkDef()``.\n\"\"\"\n# category: line charts\nimport altair as alt\nimport numpy as np\nimport pandas as pd\n\nx = np.arange(100)\nsource = pd.DataFrame({\n  'x': x,\n  'f(x)': np.sin(x / 5)\n})\n\nalt.Chart(source).mark_line(\n    point=alt.OverlayMarkDef(color=\"red\")\n).encode(\n    x='x',\n    y='f(x)'\n)\n", "path": "altair/examples/line_chart_with_points.py"}]}