Legends are great for a few reasons, but they're not so great when it comes to tagging elements in the true BIM sense. They can hold families, text, detail lines and dimensions, but when we want to add a real tag to our legend, we're stuck with dummy text.
To resolve this, some firms would create elevations of a host wall with doors and windows on a separate workset. This works fairly well; the workset can be turned of so no elements will show in any views, except for schedules where custom filters are needed to hide the legend families. Another approach is to use phases, but we have to be really careful how this is set up. Changes in Phase Filters could possibly reveal the legend families in our schedules. Neither options are fool-proof.
A safer way to create a true Legend is to use Design Options. For this to work, we'll need a dedicated Option Set with two Options, of which the primary option will remain blank. Any legend families and hosts will be added to the secondary option, and placed somewhere in the distance.
With the creation of a Design Option, the Visibility/Graphic Override dialog box now has a new tab which allows us to set which Options should be visible. By default, this is set to Automatic, which means any option that is currently set to be the Primary Option.
Since legend families and hosts are added to the secondary option, none of them will show up in a schedule. If desired, for purposes other than legends, design options can be included in schedules in the schedules' properties.
Now we can create a floor plan (working view) and elevations (legends) set to show the secondary option, and look... we can tag our families!