A measure aiming for the November ballot would make the property tax savings stemming from Proposition 13 portable. Proposition 13, the hugely consequential, four-decade-old California law, already keeps property tax increases well below the rate of home appreciation. The new initiative backed by the California Realtors Assn. would allow people who sell their homes keep their low tax rates when they move. Zocalo Public Square commentator Joe Mathews says that makes sense, if you think that aging homeowners are the most important group in California. In fact, Mathews says why not take the proposal to its logical end, by extending property tax benefits past death?