A target line is used to compare series data points values against an indicator that acts as a delimiter,
which usually represents a goal to achieve or a boundary beyond which data points might be considered as
undesired deviations.
Target lines belong to graphsets, and there is no limitation on the number of
target lines that can be added to the chart context. The applet GraphApplet, however, limits the number of target
lines to 20, in that the target lines parameters are indexed and identified by GraphApplet in an internal loop.
Target lines are linked to their respective graphsets using the parameter 'targetlinex_graphsetindex'. If this
parameter is not informed a target line is linked to the primary graphset.
Target lines are only supported by charts created with GraphApplet.