DayPilot Bubble Feature

You need to follow these steps:

1. Create the bubble:

<DayPilot:DayPilotBubble 
ID="DayPilotBubble1" 
runat="server" 
CssOnly="true"
CssClassPrefix="bubble_default"
/>

2. Assign it to the monthly calendar (http://www.daypilot.org/month.html):

<DayPilot:DayPilotMonth ....
BubbleID = "DayPilotBubble1"
/>

3. Set the bubble HTML for events (7.4 syntax):

protected void DayPilotScheduler1_BeforeEventRender(object sender, DayPilot.Web.Ui.Events.Scheduler.BeforeEventRenderEventArgs e)
{
  e.BubbleHtml = (string) e.DataItem["details"]; // assumes that your DataSource contains a field called "details"
}