Installing w3c-markup-validator removes w3c-dtd-xhtml, W3C validator needs this

[Jon Cram]

OS version: 12.10
Relevant package versions:
w3c-markup-validator:
  Installed: 1.2+dfsg-6
  Candidate: 1.2+dfsg-6
  Version table:
 *** 1.2+dfsg-6 0
        500 http://gb.archive.ubuntu.com/ubuntu/ quantal/universe amd64 Packages
        100 /var/lib/dpkg/status

w3c-dtd-xhtml:
  Installed: (none)
  Candidate: 1.1-5ubuntu1
  Version table:
     1.1-5ubuntu1 0
        500 http://gb.archive.ubuntu.com/ubuntu/ quantal/universe amd64 Packages
        100 /var/lib/dpkg/status

======

This applies to 12.10, things worked fine before upgrading from 12.04 to 12.10.

The package w3c-dtd-xhtml provides /usr/share/xml/xhtml/*. This directory contains DTDs that the W3C HTML validator depends on.

Installing w3c-markup-validator on 12.10 (as seen by myself with two machines, so perhaps a too-small sample size) removes the w3c-dtd-xhtml package. This causes the W3C HTML validator to return a HTTP 500 error when performing a validation.

Installing the w3c-dtd-xhtml package (required by the W3C HTML validator) removes the w3c-markup-validator package!

Solution:

sudo apt-get install w3c-dtd-xhtml
sudo cp -R /usr/share/xml/xhtml /usr/share/xml/xhtml.bak
sudo apt-get install w3c-markup-validator
sudo cp -R /usr/share/xml/xhtml.bak /usr/share/xml/xhtml

Ideally installing the w3c-markup-validator package should also install the w3c-dtd-xhtml and each should not remove the other as that really messes up the universe.