Name of the currently open GUI.

Can be one of the following values: * UNKNOWN * GUISTATS * GUISCREENADVANCEMENTS * GUICHAT * GUICOMMANDBLOCK * GUICONFIRMOPENLINK * GUICONTROLS * GUICREATEFLATWORLD * GUICREATEWORLD * GUICUSTOMIZESKIN * GUICUSTOMIZEWORLDSCREEN * GUIDISCONNECTED * GUIDOWNLOADTERRAIN * GUIENCHANTMENT * GUIERRORSCREEN * GUIFLATPRESETS * GUIGAMEOVER * GUIHOPPER * GUIINGAMEMENU * GUILANGUAGE * GUIMAINMENU * GUIMEMORYERRORSCREEN * GUIMERCHANT * GUIMULTIPLAYER * GUIOPTIONS * GUIREPAIR * GUISCREENADDSERVER * GUISCREENBOOK * GUISCREENCUSTOMIZEPRESETS * GUISCREENDEMO * GUISCREENOPTIONSSOUNDS * GUISCREENREALMSPROXY * GUISCREENRESOURCEPACKS * GUISCREENSERVERLIST * GUISCREENWORKING * GUISHARETOLAN * GUISLEEPMP * GUISNOOPER * GUIVIDEOSETTINGS * GUIWINGAME * GUIWORLDEDIT * GUIWORLDSELECTION * GUIYESNO * GUIBEACON * GUIBREWINGSTAND * GUICHEST * GUICONTAINERCREATIVE * GUICRAFTING * GUIDISPENSER * GUIEDITCOMMANDBLOCKMINECART * GUIEDITSIGN * GUIEDITSTRUCTURE * GUIFURNACE * GUIINVENTORY * GUISCREENHORSEINVENTORY * GUISHULKERBOX * SCREENCHATOPTIONS * GUICONNECTING