2.2.3 [XML] Section 2.5, Comments
The specification states:
Definition: Comments may appear anywhere in a document outside other markup; in addition, they may appear within the document type declaration at places allowed by the grammar. They are not part of the document's character data; an XML processor MAY, but need not, make it possible for an application to retrieve the text of comments. For compatibility, the string "--" (double-hyphen) MUST NOT occur within comments.] Parameter entity references MUST NOT be recognized within comments.
MSXML3 and MSXML6
The following clarifications apply:
Comment text can be retrieved.
A valid comment can contain a double hyphen ("--") when the double hyphen is represented by the character reference