legend.maxheight not honored in Jupyter / notebook renderer though works in browser

首先，在 Jupyter notebook 中使用 fig.show() 執行提供的 Plotly Express 範例，並使用 fig.show(renderer="browser") 執行，比較圖例與 write_html 的行為。追蹤以 notebook 為基礎的 renderer 進入點，並判斷為什麼沒有套用 legend.maxheight；當 notebook renderer 以與瀏覽器 renderer 一致的方式限制圖例時，即視為完成。

Description

I found that when using legend.maxheight in Plotly (>= 6.3), it works as expected when rendering via browser (e.g. fig.show(renderer="browser") or write_html). However, when using Jupyter Notebook (or similar notebook-based renderers), the maxheight setting is ignored / not reflected — the legend expands or overflows as if maxheight were not applied.

This inconsistent behavior suggests that the notebook renderer is not honoring legend.maxheight, which hampers consistent formatting of legends in notebook environments.

Code Example to Reproduce

import plotly.express as px
from plotly import data

df = data.gapminder().query("year==2007 and continent == 'Europe'")

fig = px.scatter(
    df,
    x="gdpPercap",
    y="lifeExp",
    color="country",
    size="pop",
    size_max=45,
    title="Life Expectancy vs. GDP per Capita in 2007 (by Country)",
    labels={"gdpPercap": "GDP per Capita"},
)

fig.update_layout(
    xaxis=dict(side="top"),
    legend=dict(
        orientation="h",
        yanchor="bottom",
        y=-0.35,
        xanchor="center",
        x=0.5,
        maxheight=0.005,  # comment out this line to see legend take up ~0.5 of plotting area
        title_text="Country"
    ),
)
# Display inline in notebook
fig.show()

# Display via browser
fig.show(renderer="browser")

When executed:

• In browser renderer, the legend is constrained in height per the maxheight=0.005 setting (i.e. 0.5% of plotting height).
• In notebook renderer, the legend is not constrained and expands beyond that, ignoring the maxheight.

Expected Behavior

The legend.maxheight setting should be honored consistently across all renderers, including the notebook-based inline renderers inside Jupyter or related environments. That is, legends should be constrained to the height specified by maxheight, even when showing inline.