preferred_name: 3-O-{beta-D-GlcA-(1->[3)-alpha-D-Xyl-(1->3)-beta-D-GlcA-(1->](n)-4)-beta-D-Xyl-(1->4)-Rib-ol-P-Rib-ol-P-3-beta-D-GalNAc-(1->3)-beta-D-GlcNAc-(1->4)-O-6-P-alpha-D-Man}-L-Thr-[protein] + UDP-alpha-D-xylose = 3-O-{(1->[3)-alpha-D-Xyl-(1->3)-beta-D-GlcA-(1->](n+1)-4)-beta-D-Xyl-(1->4)-Rib-ol-P-Rib-ol-P-3-beta-D-GalNAc-(1->3)-beta-D-GlcNAc-(1->4)-O-6-P-alpha-D-Man}-L-Thr-[protein] + UDP + H(+)