These pages outline the chart configuration options, and the methods and properties of Highcharts objects.
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Callback JavaScript function to format the annotation's
label. Note that if a format or text are defined,
the format or text take precedence and the formatter is
ignored. This refers to a point object. The callback also receives
an argument ctx so that arrow-functions can access the same
context (the point in this case) as normal functions can using
this. Since v12.6.0, the callback receives ctx.