In the Guidelines, 188.8.131.52 says:
"A bibliographic description, particularly for an analytic title, will often include some additional information specifying its location, for example as a volume number, page number, range of page numbers, or name or number of a subdivision of the host work. The element biblScope may be used to identify such information if it is present. Where it is desired to distinguish different classes of such information (volume number, page number, chapter number, etc.), the type attribute may be used with any convenient typology.
"When the item being cited is a journal article, the imprint element describing the issue in which it appeared may contain biblScope elements for volume and page numbers, together with a date element."
I believe the first paragraph explains how to use a <biblScope> that is not a child of <imprint>, and the second paragraph describes a <biblScope> which is a child of <imprint>. What makes the description of a journal article different from the description of an analytic title? I thought a journal article's title is a type of analytic title.
So there are a few things that need clarification:
1) Whether the first paragraph's directions about use of biblScope really means to say that it is a sibling, not child, of imprint.
2) Why a journal article is different from an analytic title (or other analytic titles).
3) Whether, in the case of a journal article, there should be a biblScope sibling of imprint in addition to a child. It seems that the sibling biblScope would have the page numbers cited and the child biblScope would have the page numbers of the whole article.