docs: add example with overlapping bars in a grouped bar chart

tests/examples_arguments_syntax/grouped_bar_chart_overlapping_bars.py

@@ -0,0 +1,27 @@
+"""
+Grouped Bar Chart with xOffset and overlapping bars
+---------------------------------------------------
+Like :ref:`gallery_grouped_bar_chart2`, this example shows a grouped bar chart using the ``xOffset`` encoding channel, but in this example the bars are partly overlapping within each group.
+"""
+# category: bar charts
+import altair as alt
+import pandas as pd
+
+source = pd.DataFrame(
+    {
+        "category": list("AABBCC"),
+        "group": list("xyxyxy"),
+        "value": [0.1, 0.6, 0.7, 0.2, 0.6, 0.1],
+    }
+)
+
+base = alt.Chart(source, width=alt.Step(12)).encode(
+    x="category:N",
+    y="value:Q",
+    xOffset=alt.XOffset("group:N", scale=alt.Scale(paddingOuter=0.5)),
+)
+
+alt.layer(
+    base.mark_bar(size=20, stroke="white", fillOpacity=0.9).encode(fill="group:N"),
+    base.mark_text(dy=-5).encode(text="value:Q"),
+)

tests/examples_methods_syntax/grouped_bar_chart_overlapping_bars.py

@@ -0,0 +1,27 @@
+"""
+Grouped Bar Chart with xOffset and overlapping bars
+---------------------------------------------------
+Like :ref:`gallery_grouped_bar_chart2`, this example shows a grouped bar chart using the ``xOffset`` encoding channel, but in this example the bars are partly overlapping within each group.
+"""
+# category: bar charts
+import altair as alt
+import pandas as pd
+
+source = pd.DataFrame(
+    {
+        "category": list("AABBCC"),
+        "group": list("xyxyxy"),
+        "value": [0.1, 0.6, 0.7, 0.2, 0.6, 0.1],
+    }
+)
+
+base = alt.Chart(source, width=alt.Step(12)).encode(
+    x="category:N",
+    y="value:Q",
+    xOffset=alt.XOffset("group:N").scale(paddingOuter=0.5),
+)
+
+alt.layer(
+    base.mark_bar(size=20, stroke="white", fillOpacity=0.9).encode(fill="group:N"),
+    base.mark_text(dy=-5).encode(text="value:Q"),
+)