I want to be able to label areas in a page so I may later query the labels across the docs. For example, as I define a series of "How to " wiki pages, whenever I confront a gap I'd like to label it as such right in the page. From what I'm reading labels appear to be scoped at the whole page level, or to attachments.
You are right unfortunately - labels are attached to a whole page - rather than segments on a page.
There's no specific method to relate to labels in a section of a page - other than writing a unique word / phrase and searching for it later.