1H-2,1-Benzothiazine-7-carboxylic acid,3-[5-(7-carboxy-4-hydroxy-1-methyl-2,2-dioxido-1H-2,1-benzothiazin-3-yl)-3-methyl-2,4-pentadienylidene]-3,4-dihydro-1-methyl-4-oxo-,2,2-dioxide