Catalyzes the hydrolysis of the internal glycosidic bonds in heteroxylans, releasing mainly xylobiose and xylotriose. Most active on oat-spelt xylan. Endohydrolysis of (1->4)-beta-D-xylosidic linkages in xylans. Optimum pH is 6-8. Optimum temperature is 40-50 degrees Celsius. Glycan degradation; xylan degradation. Monomer. Belongs to the glycosyl hydrolase 10 (cellulase F) family.