This option is useful when TinyMCE is used within tabs in MSIE. This property is needed since MSIE has a bug where it's impossible to retrive the width/height on elements like images while it's hidden using display:none. So use this property to define the class name that is used to hide a specific tab, this will help TinyMCE to display the tab while getting the image data.
Example of usage of the display_tab_class option:
tinyMCE.init({ ... display_tab_class : "showTab" });