doc: add stackPercent apache/echarts#20910

en/option/series/bar.md

@@ -157,6 +157,12 @@ How to stack values if the [stack](~series-bar.stack) property has been set. Opt
 + `'positive'`: only stack positive values.
 + `'negative'`: only stack negative values.
 
+## stackPercent(boolean) = false
+
+When enabled and `stack` is used, stacked values will be normalized as percentages of the total at each category. Each stack will add up to 100%.
+
+Both the raw value and the normalized percentage will be displayed in the tooltip. Use `params.percent` to access the normalized value in tooltip and label formatters.
+
 ## sampling(string)
 
 The downsampling strategy used when the data size is much larger than pixel size. It will improve the performance when turned on. Defaults to be turned off, indicating that all the data points will be drawn.

en/option/series/line.md

@@ -83,6 +83,12 @@ How to stack values if the [stack](~series-line.stack) property has been set. Op
 
 {{ use: partial-cursor() }}
 
+## stackPercent(boolean) = false
+
+When enabled and `stack` is used, stacked values will be normalized as percentages of the total at each category. Each stack will add up to 100%.
+
+Both the raw value and the normalized percentage will be displayed in the tooltip. Use `params.percent` to access the normalized value in tooltip and label formatters.
+
 ## connectNulls(boolean) = false
 
 <ExampleUIControlBoolean />

zh/option/series/bar.md

@@ -233,6 +233,12 @@ option = {
 + `'positive'` 只堆积正值。
 + `'negative'` 只堆叠负值。
 
+## stackPercent(boolean) = false
+
+启用此选项并使用 `stack` 后，堆叠值将被标准化为每个类别总计的百分比。每个堆叠值的总和将达到 100%。
+
+原始值和标准化百分比都将显示在工具提示中。使用 `params.percent` 可在工具提示和标签格式化程序中访问标准化值。
+
 ## sampling(string)
 
 柱状图在数据量远大于像素点时候的降采样策略，开启后可以有效的优化图表的绘制效率，默认关闭，也就是全部绘制不过滤数据点。

zh/option/series/line.md

@@ -110,6 +110,12 @@ const option = {
 
 {{ use: partial-cursor() }}
 
+## stackPercent(boolean) = false
+
+启用此选项并使用 `stack` 后，堆叠值将被标准化为每个类别总计的百分比。每个堆叠值的总和将达到 100%。
+
+原始值和标准化百分比都将显示在工具提示中。使用 `params.percent` 可在工具提示和标签格式化程序中访问标准化值。
+
 ## connectNulls(boolean) = false
 
 <ExampleUIControlBoolean />