Targets are a set of constants used primarily by the navigation commands that permit the expression
of such concepts as "open in a new buffer", "open in a new window", "open in a new background buffer",
"open in the current buffer", et cetera.  Targets are also used to configure the behavior of some
special buffers, including download-manager buffers.  The user variable
"download_buffer_automatic_open_target" uses a target to configure the behavior of how to open
new download-manager buffers.

Window tags are the unique identifiers that conkeror assigns to each conkeror window.  A window can
be looked up by its tag.

This feature request is to expand the targets system with a mechanism for specifying window tags, such
that targets can refer to a specific *existing* object in which to load a resource.  Currently the
targets system only has the means of referring to the current buffer, new buffers, and new windows,
but not specific existing windows and buffers.

As a correlative issue to this one is assigning unique tags to every buffer, so that specific buffers
could also be referred to as target.