This is essentially an editorial comment on Serialization section 5.

Firstly, I think the phrase

The result of serialization MUST be such that the reconstructed tree may be
different than the result tree as follows:

should be

The result of serialization MUST be such that the reconstructed tree is the same
as the result tree except for the following permitted differences:

When we get to the phrase:

A consequence of this rule is that certain characters MUST be output as
character references,

one is currently left asking "which rule?", especially as this paragraph appears
to be part of the last item in the list of permitted differences. The paragraph
should not be indented, and the rule referred to is the one that the two trees
must be the same except for certain permitted differences.