It seems that every time I set up a project in Eclipse PDT I run up against the problem of a bunch XML errors being generated from deep inside some third party library somewhere.
Searching Google shows lots of advice saying you need to go to Preferences>Validators and clicking "Suspend all validators".
The trouble is that there is no 'Validators' option in that location.
It seems that to turn off this unwanted validation you need to first install
"Eclipse XML Editors and Tools".
Why Eclipse will try and do the validation in the first place without this module installed is a question for another day.
Once you have installed that you can follow the normal steps to "Suspend all Validators" (either globally or for individual projects) as described everywhere on the Intertubes.
One final thing though, be aware that after suspending the validators, you must right-click the project and click "Validate" to remove all the nasty red marks.