in HTML5 the body element is defined thus :
"The body element represents the main content of the document."
In HTML 4 it was defined thus :
"The body of a document contains the document's content."
The HTML 4 definition matches reality, the body element contains the 'content' of the document not just the 'main content' of the document.
suggest removing the word 'main' from the HTML5 definition to match HTML 4.0 definition:
"The body element represents the content of the document."
have made change in fork of the spec as it is part of the changes required to add the main element to 5.1
closing as was fixed by https://www.w3.org/Bugs/Public/show_bug.cgi?id=20309#c6