Endo-acting enzyme that randomly cleaves the internal xylosidic linkages of the xylan backbone, yielding xylooligosaccharides of various lengths which are further hydrolyzed to xylose molecules by beta-xylosidase (EC 3.2.1.37). Requires at least three xylose residues for catalytic activity. Does not have activity against xylobiose. Endohydrolysis of (1->4)-beta-D-xylosidic linkages in xylans. Optimum pH is 5.5. Optimum temperature is 70 degrees Celsius. Glycan degradation; xylan degradation. By xylan and xylose. Belongs to the glycosyl hydrolase 10 (cellulase F) family.