Commit two new docs: loose-vs-strict and proprietary-tags, both research/reference.

git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@554 48356398-32a2-884e-a903-53898d9a118a

docs/ref-loose-vs-strict.txt

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+
+Loose versus Strict
+    Changes from one doctype to another
+
+There are changes.  Wow, how insightful.  Not everything changed is relevant
+to HTML Purifier, though, so let's take a look:
+
+== Major incompatibilities ==
+
+BLOCKQUOTE changes from 'flow' to 'block'
+    behavior: inline inner contents should not be nuked, paragraph as necessary
+U, S, STRIKE cut
+    behavior: replace with appropriate inline span + CSS
+ADDRESS from potpourri to Inline (removes p tags)
+    behavior: p tags silently dropped or replaced with something
+
+== Things we can loosen up ==
+
+Tags DIR, MENU, CENTER, ISINDEX, FONT, BASEFONT? allowed in loose
+Attributes allowed in loose:
+    div,p,h#.align
+    ul,ol.type
+    ul,ol,dl.compact
+    ol.start
+    li.type,value
+    hr.align,noshade,size,width
+    pre.width
+    img.name?,align,border,hspace,vspace
+    table.align,bgcolor
+    caption.align
+    tr.bgcolor
+    th,td.nowrap,bgcolor,width,height
+
+== Periphery issues ==
+
+A tag's attribute 'target' (for selecting frames) cut
+    behavior: shouldn't be needed, use loose doctype if needed
+OL/LI tag's attribute 'start' (for renumbering lists) cut
+    behavior: no substitute, just delete
+Attribute 'name' deprecated in favor of 'id'
+    behavior: create proper AttrTransform
+PRE tag allows SUB/SUP? (strict dtd comment vs syntax, loose disallows)

docs/ref-proprietary-tags.txt

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+
+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)
+<multicol>, multiple columns
+<nobr>, no linebreaks
+<spacer>, whitespace in doc
+<wbr>, allows linebreaks
+
+<listing>, monospace pre-variant (extremely rare)
+<plaintext>, escapes all tags to the end of document
+<ruby> and friends, (more research needed, appears to be XHTML 1.1 markup)
+<xmp>, monospace, replace with pre