REGRESSION (r76301): 'plaintext-only' must be a supported contentEditable mode.
<rdar://problem/8913952>
Despite not being in the spec, pre-existing WebKit clients rely on setContentEditable:'plaintext-only'. Patch forthcoming.
Created attachment 81707 [details] Patch
Oops, I forgot expected results. I'll include those when I land.
Committed r77985: <http://trac.webkit.org/changeset/77985>