Proprietary Tags <nobr> and friends Here are some proprietary tags that W3C does not define but occasionally show up in the wild. We have only included tags that would make sense in an HTML Purifier context. <align>, block element that aligns (extremely rare) <blackface>, inline that double-bolds text (extremely rare) <comment>, hidden comment for IE and WebTV <multicol cols=number gutter=pixels width=pixels>, multiple columns <nobr>, no linebreaks <spacer align=* type="vertical|horizontal|block">, whitespace in doc, use width/height for block and size for vertical/horizontal (attributes) (extremely rare) <wbr>, potential word break point: allows linebreaks. Only works in <nobr> <listing>, monospace pre-variant (extremely rare) <plaintext>, escapes all tags to the end of document <xmp>, monospace, replace with pre These should be put into their own Tidy module, not loaded by default(?). These all qualify as "lenient" transforms.