The following text from the (Help | Help Contents) Checking an XML Document for Well-Formedness documentations should be refined.

The following...

- Every start tag must have an end tag. 
- Elements cannot overlap. 
- There must be exactly one root element. 
- Attribute values must be quoted. 
- An element cannot have two attributes with the same name. 
- Comments and processing instructions cannot appear inside tags. 
- No unescaped < or & signs can occur in the element's character data or attribute's character data. 

should read something similar to...

- Every start tag must have a matching end tag. Tags are case-sensitive. 
- Start, end and empty-element tags must have proper nesting, without missing or overlapping tags. 
- There must be exactly one root element, also known as the document element, that does not appear in the content of any other element. 
- Attribute values must be quoted.  Attributes are listed in the start tag. 
- An element cannot have two or more attributes with the same name. 
- Comments and processing instructions cannot appear inside tags. 
- Special syntax characters including  "<" and "&" [[PLEASE COMPLETE AS ABOVE REFERENCE IS WRONG, (e.g. "&amp;" can occur in the character data).  See reference below for ideas.]]. 

Thanks.

Reference: 
http://en.wikipedia.org/wiki/XML#Well-formedness_and_error-handling