Tooltip in 'timelineAndSentimentChart.js' is relatively generalized. Mainly the tooltip is designed for markers. For line series, there is an 'interactiveLayer' which can be enabled. By default, the interactiveLayer is disabled.
'tooltipContent' can be a function, which would be used for all the marker tooltip
'tooltipContent' can be array of functions. In such a case, if 'showTooltip' is defined for a series then the value is used as an index to the array of functions to pick the correct function. If 'showTooltip' = -1, then no tooltip will be displayed for those set of markers. If 'showTooltip' is not defined, then the first function in the array of functions will be used.