Originally Posted by dgatwood
Have you tried -webkit-hyphens on the actual device? Because it does work in Kindle Previewer, and I would hope that they used the same version of GTK WebKit....
KindlePreviewer is utterly unreliable. It often shows support for formatting not available on the actual devices and vice versa.
On eInk Kindles soft-hyphens work, but automatic hyphenation does not
work no matter what hypenation style you use. You may want to test Kindle books on actual devices or the Kindle for PC app before making blanket statements.