Endohydrolysis of (1->4)-beta-D-xylosidic linkages in xylans. Optimum temperature is 70 degrees Celsius. Thermostable. Glycan degradation; xylan degradation. XynA is a modular enzyme. The number of CBM6 (carbohydrate binding type-6) domains varies between strains. The polymeric substrate can interact with several of these CBM6 domains (By similarity). Belongs to the glycosyl hydrolase 11 (cellulase G) family.