|a structure demolished|
|Definition:||Indicates that the structure where the tag belongs to, has been demolished. The value added to the tag should be a date|
Obsolete, it is now common to use "demolished" as namespace prefix to achieve this particular functionality, eg "demolished:building=yes". See Comparison of life cycle concepts for other alternatives.
ex. demolished=2008-02-15 ("demolished=YYYY-MM-DD")
Instead of just deleting structures with an editor, marking them as demolished should add a fourth dimension to Openstreetmaps, meaning time. Having the same map contain temporal data means that a past situation could be reviewed, as well as a future "planned" situation as well.
Note: moved from the template of validated tags to this proposal. Start a vote if you want it "approved" (keeping nonexistent objects for historical purpose is very controversial within the OSM community).