Gets or sets the rule that determines the text box height.
An enumeration member that specifies how to determine the text box height.
The default value of the HeightRule property is TextBoxSizeRule.Auto and the text box is stretched horizontally to fit its content if necessary. If you set the HeightRule property to TextBoxSizeRule.Exact, the text box retains its size as specified by the Size property.
When a text box is resized by an end user, the HeightRule property is set to TextBoxSizeRule.Exact.