Man pages matching name xkbsaredirectvmodsmask in section 3:

XkbSARedirectVModsMask.3.en	debian 10 / libx11-doc
XkbSARedirectVModsMask.3.en	debian 11 / libx11-doc
XkbSARedirectVModsMask.3.en	debian 12 / libx11-doc