[VE][html5] explaining why "&" is invalid in href value

Validating http://www.michelesalvador.it/u/
Error [html5]: "& did not start a character reference. (& probably 
should have been escaped as &.)"

In my webpage I have a lot of "&" in href attribute
something like this:  <a href="?one=foo&two=bar">
and validator properly reports them as errors

My suggestion is to provide some brief explanation of why '&' is 
incorrect in href value and should be replaced with &amp;
something like http://htmlhelp.com/tools/validator/problems.html#amp

thank you
Michele Salvador, Italy