Any time the book referencing attribute is used in a page,
permanently tag that page with the `ref-extends` property, so
that it can be watched and cleaned up if necessary.
Bug: T237531
Change-Id: Ice5d9d8f7a305702cdc7c2a55d4147c4f79b5881
Incremental patch which extracts the refines attribute from the tag.
Doing this now to allow the calling function to have responsibility
for doing something with the attribute value.
Bug: T237531
Change-Id: I59bb409bedd8e6ed06268e705e02e8ffb45b1f0e
Note this is intentionally testing a private method. As of now, the
code is so heavily entangled, it's not yet possible to test individual
aspects without calling private methods. The plan is to slowly increase
the overall test coverage, and the start restructuring the code as
necessary.
Change-Id: Ib3b01bddaffd0469fb66979c67c8114a5807df6d
