# Welcome to the Highcharts Gantt JS (gantt) Options Reference

These pages outline the chart configuration options, and the methods and properties of Highcharts objects.

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# series.xrange.tooltip.dateTimeLabelFormats

For series on datetime axes, the date format in the tooltip's header will by default be guessed based on the closest data points. This member gives the default string representations used for each unit. For an overview of the string or object configuration, see dateFormat.