Hello, The documentation of the STL is no longer on sgi.com. So the link to `PairAssociativeContainer` [here ](https://github.com/boostorg/property_map/blob/e3a3c3655f4118fd15a02d8315f86a48db7390fd/doc/const_assoc_property_map.html#L30) should better go to the local copy hosted by boost.org, that is to https://www.boost.org/sgi/stl/PairAssociativeContainer.html