set the toolTip of <object> to <string>
set the toolTip of button "OK" to "Click to accept the result"
set the toolTip of me to field "Explanation"
set the toolTip of me to "Hello" & return & "World!"
A tool tip is a small box containing some text, which pops up on the screen when the mouse pointer hovers over a control. The text briefly explains the purpose and use of the control.
The tool tip appears when the mouse pointer is within the control's rectangle and when the mouse has not moved for the time specified by the toolTipDelay property. If the mouse is moving, the tool tip does not appear.
Tool tips should be short and should not attempt to explain the entire action of the control. They are best used as a short reminder or clue about what a control does.
Tool tips appear only when the Browse tool is selected.
As of LiveCode version 2.7.4 toolTips can be multiline strings. Previous version restrict tooltips to single lines.