Html support for Group 's Title (tooltip) on vis-timeline

[nhamthanh]

Now I need to display html format for group 's title (tooltip) when user hover. But it look like vis-timeline doesn't support , the tooltip now stick with title property and must be plain text.
The HTML format simple:
. list1
. list2
And tooltip display on top ( not bottom position) of group like overflow-cap of items.

Do you have any suggest that group tooltip can be formatted like items. Or I can do any thing to work around ?