These pages outline the chart configuration options, and the methods and properties of Highcharts objects.
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The HTML of the tooltip header line. Variables are enclosed by
curly brackets. Available variables are point.key, series.name,
series.color and other members from the point and series
objects. The point.key variable contains the category name, x
value or datetime string depending on the type of axis. For datetime
axes, the point.key date format can be set using
tooltip.xDateFormat.