The function is called by the Timeline with an items' data as the first argument, the item element as the second argument and the edited data as the third argument, and must return HTML code, a string or a template as result.
When the option template is specified, the items do not need to have a field A template function used to generate the visible frame of the items.
The time scale on the axis is adjusted automatically, and supports scales ranging from milliseconds to years.
On load, the Timeline will render all items once to determine their width and height.
Keep the number of items in this configuration limited to a maximum of a few hundred items.
If undefined, the Timeline will auto detect the type from the items data: if a start and end date is available, a 'range' will be created, and else, a 'box' is created. A template function used to generate the contents of the tooltip.
The function is called by the Timeline with an item data as the first argument, and must return HTML code, a string or a template as result. value (rather than inheriting from the timeline level).
This allows for flexible customization using css styling. When the group column is provided, all items with the same group are placed on one line. Grouping items can be useful for example when showing availability of multiple people, rooms, or other resources next to each other.