Hi Matteo,
1) The timeline header can be customized using the timnelineHeaderFormatFunction. You can set a custom formatting function to that property in order to customize the text displayed in each cell inside the header. The function contains the following arguments (date, type, isHeaderDetails).

  • date – the date that will be displayed inside the cell.
  • type – is the view type for the date (year, month, week, day, hour)
  • isHeaderDetails – a flag indicating whether this is a cell from the header details container(the first level of the header inside the timeline) or the second.

Here’s a demo on how to customize the dates in the header.
2) This feature is currently unavailable but we will include it in a future release. Currently we are working on a new major feature for the Gantt Chart – Resource management.
3) The window for task editing can be completely customized via the popupWindowCustomizationFunction. It accepts a callback with three arguments:

  • target – the actual window.
  • type – the type of editing ( ‘task’ or ‘connection’ are currently supported)
  • taskIndex – the index of the task that is going to be edited.

Here is a demo showing how to customized the task editor.
We have a tutorial on how to create and apply settings on the elements using Vue.js. Here’s the link.
You can also customize the property editors for each task column using the customEditor property on specific taskColumns. Here’s an example on that.
Best Regards,
Smart HTML Elements Team