w3c-markup-validator from openSUSE:Backports:SLE-15 project
Select Your Operating System
Add repository and install manually
For standard run the following as root:
zypper addrepo https://download.opensuse.org/repositories/openSUSE:Backports:SLE-15/standard/openSUSE:Backports:SLE-15.repo zypper refresh zypper install w3c-markup-validator