By default, toolbar buttons do not have a popup that displays a tooltip or onhover text to the user. If you wish to do so, you can add a tag in the toolbar .ascx file that will show a tooltip. This is the Title tag. As an example, I have added the Title tag to the Sign Out button that appears on a standard toolbar below:
<pw:ToolbarClientButton HorizontalAlign="Left" OnClientClick="return SignOut();" Text="Sign Out" Title="Leaving the Portal" Icon="images/nav_right_green.png"
runat="server" TabIndex="2" />
When hovering over the text Sign Out, it will pop up with a tooltip saying "Leaving the Portal".
The downside to this method is the tooltip only occurs when hovering over the text of the button. Hovering over the image does not bring it up. This is an issue for customers who wish to have textless buttons.
If you wish to have a textless button with a popup, the best way to do it is to forego the ToolbarClientButton that is used in the default toolbars and go with straight HTML:
<img src="ImageGallery/Icons/balloon.gif" Title="Leaving the Portal" onClick="return SignOut();" style="cursor:pointer" />
This will put an image there with a tooltip and change the cursor to be a pointer when hovering over it.