chart (event tokens):
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The clicked field name is the name of the field or series for the y-Axis if present (similar to click.name2). If the name of the field or series is not available the field or category for the x-axis is used (click.name).
Data Property Description
click.name Name of the field or category for the x-axis. Not available when the legend has been clicked.
click.value Value of the field or category for the x-axis. Not available when the legend has been clicked.
click.name2 Name of the field or series for the y-axis.
click.value2 Value of the field or series for the y-axis. Not available when the legend has been clicked.
row. Any field values along the y-axis at the same point as the click on the x-axis. Not available when the legend has been clicked.
row. Value of the x-axis. Not available when the legend has been clicked.
earliest/latest Time range of the clicked chart segment, or if not applicable, the time range of the search.
For more details at http://docs.splunk.com/Documentation/Splunk/6.2.1/Viz/PanelreferenceforSimplifiedXML
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