documentation for #1274
documentation for #1274

mtraynham/dc.js,mtraynham/dc.js,aaronhoffman/dc.js,dc-js/dc.js,aaronhoffman/dc.js,dc-js/dc.js,dc-js/dc.js,mtraynham/dc.js,aaronhoffman/dc.js,aaronhoffman/dc.js,mtraynham/dc.js,mtraynham/dc.js,aaronhoffman/dc.js,dc-js/dc.js,dc-js/dc.js