267 lines
12 KiB
Haskell
267 lines
12 KiB
Haskell
{-# LANGUAGE OverloadedStrings #-}
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-- | Sanatize HTML to prevent XSS attacks.
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--
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-- See README.md <http://github.com/gregwebs/haskell-xss-sanitize> for more details.
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module Text.HTML.SanitizeXSS
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(
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-- * Sanitize
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sanitize
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, sanitizeBalance
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, sanitizeXSS
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-- * Custom filtering
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, filterTags
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, safeTags
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, balanceTags
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-- * Utilities
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, sanitizeAttribute
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, sanitaryURI
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) where
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import Text.HTML.SanitizeXSS.Css
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import Text.HTML.TagSoup
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import Data.Set (Set(), member, notMember, (\\), fromList, fromAscList)
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import Data.Char ( toLower )
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import Data.Text (Text)
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import qualified Data.Text as T
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import Network.URI ( parseURIReference, URI (..),
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isAllowedInURI, escapeURIString, uriScheme )
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import Codec.Binary.UTF8.String ( encodeString )
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import qualified Data.Map as Map
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import Data.Maybe (catMaybes)
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-- | Sanitize HTML to prevent XSS attacks. This is equivalent to @filterTags safeTags@.
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sanitize :: Text -> Text
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sanitize = sanitizeXSS
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-- | alias of sanitize function
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sanitizeXSS :: Text -> Text
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sanitizeXSS = filterTags safeTags
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-- | Sanitize HTML to prevent XSS attacks and also make sure the tags are balanced.
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-- This is equivalent to @filterTags (balanceTags . safeTags)@.
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sanitizeBalance :: Text -> Text
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sanitizeBalance = filterTags (balanceTags . safeTags)
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-- | Filter which makes sure the tags are balanced. Use with 'filterTags' and 'safeTags' to create a custom filter.
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balanceTags :: [Tag Text] -> [Tag Text]
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balanceTags = balance Map.empty
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-- | Parse the given text to a list of tags, apply the given filtering function, and render back to HTML.
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-- You can insert your own custom filtering but make sure you compose your filtering function with 'safeTags'!
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filterTags :: ([Tag Text] -> [Tag Text]) -> Text -> Text
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filterTags f = renderTagsOptions renderOptions {
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optMinimize = \x -> x `member` voidElems -- <img><img> converts to <img />, <a/> converts to <a></a>
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} . f . canonicalizeTags . parseTags
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voidElems :: Set T.Text
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voidElems = fromAscList $ T.words $ T.pack "area base br col command embed hr img input keygen link meta param source track wbr"
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balance :: Map.Map Text Int -> [Tag Text] -> [Tag Text]
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balance m [] =
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concatMap go $ Map.toList m
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where
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go (name, i)
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| noClosing name = []
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| otherwise = replicate i $ TagClose name
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noClosing = flip member voidElems
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balance m (t@(TagClose name):tags) =
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case Map.lookup name m of
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Nothing -> TagOpen name [] : TagClose name : balance m tags
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Just i ->
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let m' = if i == 1
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then Map.delete name m
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else Map.insert name (i - 1) m
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in t : balance m' tags
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balance m (TagOpen name as : tags) =
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TagOpen name as : balance m' tags
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where
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m' = case Map.lookup name m of
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Nothing -> Map.insert name 1 m
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Just i -> Map.insert name (i + 1) m
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balance m (t:ts) = t : balance m ts
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-- | Filters out any usafe tags and attributes. Use with filterTags to create a custom filter.
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safeTags :: [Tag Text] -> [Tag Text]
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safeTags [] = []
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safeTags (t@(TagClose name):tags)
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| safeTagName name = t : safeTags tags
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| otherwise = safeTags tags
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safeTags (TagOpen name attributes:tags)
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| safeTagName name = TagOpen name
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(catMaybes $ map sanitizeAttribute attributes) : safeTags tags
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| otherwise = safeTags tags
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safeTags (t:tags) = t:safeTags tags
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safeTagName :: Text -> Bool
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safeTagName tagname = tagname `member` sanitaryTags
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safeAttribute :: (Text, Text) -> Bool
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safeAttribute (name, value) = name `member` sanitaryAttributes &&
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(name `notMember` uri_attributes || sanitaryURI value)
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-- | low-level API if you have your own HTML parser. Used by safeTags.
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sanitizeAttribute :: (Text, Text) -> Maybe (Text, Text)
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sanitizeAttribute ("style", value) =
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let css = sanitizeCSS value
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in if T.null css then Nothing else Just ("style", css)
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sanitizeAttribute attr | safeAttribute attr = Just attr
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| otherwise = Nothing
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-- | Returns @True@ if the specified URI is not a potential security risk.
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sanitaryURI :: Text -> Bool
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sanitaryURI u =
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case parseURIReference (escapeURI $ T.unpack u) of
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Just p -> (null (uriScheme p)) ||
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((map toLower $ init $ uriScheme p) `member` safeURISchemes)
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Nothing -> False
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-- | Escape unicode characters in a URI. Characters that are
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-- already valid in a URI, including % and ?, are left alone.
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escapeURI :: String -> String
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escapeURI = escapeURIString isAllowedInURI . encodeString
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safeURISchemes :: Set String
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safeURISchemes = fromList acceptable_protocols
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sanitaryTags :: Set Text
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sanitaryTags = fromList (acceptable_elements ++ mathml_elements ++ svg_elements)
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\\ (fromList svg_allow_local_href) -- extra filtering not implemented
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sanitaryAttributes :: Set Text
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sanitaryAttributes = fromList (allowed_html_uri_attributes ++ acceptable_attributes ++ mathml_attributes ++ svg_attributes)
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\\ (fromList svg_attr_val_allows_ref) -- extra unescaping not implemented
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allowed_html_uri_attributes :: [Text]
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allowed_html_uri_attributes = ["href", "src", "cite", "action", "longdesc"]
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uri_attributes :: Set Text
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uri_attributes = fromList $ allowed_html_uri_attributes ++ ["xlink:href", "xml:base"]
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acceptable_elements :: [Text]
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acceptable_elements = ["a", "abbr", "acronym", "address", "area",
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"article", "aside", "audio", "b", "big", "blockquote", "br", "button",
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"canvas", "caption", "center", "cite", "code", "col", "colgroup",
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"command", "datagrid", "datalist", "dd", "del", "details", "dfn",
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"dialog", "dir", "div", "dl", "dt", "em", "event-source", "fieldset",
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"figcaption", "figure", "footer", "font", "form", "header", "h1", "h2",
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"h3", "h4", "h5", "h6", "hr", "i", "img", "input", "ins", "keygen",
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"kbd", "label", "legend", "li", "m", "main", "map", "menu", "meter", "multicol",
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"nav", "nextid", "ol", "output", "optgroup", "option", "p", "pre",
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"progress", "q", "s", "samp", "section", "select", "small", "sound",
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"source", "spacer", "span", "strike", "strong", "sub", "sup", "table",
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"tbody", "td", "textarea", "time", "tfoot", "th", "thead", "tr", "tt",
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"u", "ul", "var", "video"]
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mathml_elements :: [Text]
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mathml_elements = ["maction", "math", "merror", "mfrac", "mi",
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"mmultiscripts", "mn", "mo", "mover", "mpadded", "mphantom",
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"mprescripts", "mroot", "mrow", "mspace", "msqrt", "mstyle", "msub",
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"msubsup", "msup", "mtable", "mtd", "mtext", "mtr", "munder",
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"munderover", "none"]
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-- this should include altGlyph I think
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svg_elements :: [Text]
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svg_elements = ["a", "animate", "animateColor", "animateMotion",
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"animateTransform", "clipPath", "circle", "defs", "desc", "ellipse",
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"font-face", "font-face-name", "font-face-src", "g", "glyph", "hkern",
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"linearGradient", "line", "marker", "metadata", "missing-glyph",
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"mpath", "path", "polygon", "polyline", "radialGradient", "rect",
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"set", "stop", "svg", "switch", "text", "title", "tspan", "use"]
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acceptable_attributes :: [Text]
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acceptable_attributes = ["abbr", "accept", "accept-charset", "accesskey",
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"align", "alt", "autocomplete", "autofocus", "axis",
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"background", "balance", "bgcolor", "bgproperties", "border",
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"bordercolor", "bordercolordark", "bordercolorlight", "bottompadding",
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"cellpadding", "cellspacing", "ch", "challenge", "char", "charoff",
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"choff", "charset", "checked", "class", "clear", "color",
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"cols", "colspan", "compact", "contenteditable", "controls", "coords",
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-- "data", TODO: allow this with further filtering
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"datafld", "datapagesize", "datasrc", "datetime", "default",
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"delay", "dir", "disabled", "draggable", "dynsrc", "enctype", "end",
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"face", "for", "form", "frame", "galleryimg", "gutter", "headers",
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"height", "hidefocus", "hidden", "high", "hreflang", "hspace",
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"icon", "id", "inputmode", "ismap", "keytype", "label", "leftspacing",
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"lang", "list", "loop", "loopcount", "loopend",
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"loopstart", "low", "lowsrc", "max", "maxlength", "media", "method",
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"min", "multiple", "name", "nohref", "noshade", "nowrap", "open",
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"optimum", "pattern", "ping", "point-size", "prompt", "pqg",
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"radiogroup", "readonly", "rel", "repeat-max", "repeat-min",
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"replace", "required", "rev", "rightspacing", "rows", "rowspan",
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"rules", "scope", "selected", "shape", "size", "span", "start",
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"step",
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"style", -- gets further filtering
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"summary", "suppress", "tabindex", "target",
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"template", "title", "toppadding", "type", "unselectable", "usemap",
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"urn", "valign", "value", "variable", "volume", "vspace", "vrml",
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"width", "wrap", "xml:lang"]
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acceptable_protocols :: [String]
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acceptable_protocols = [ "ed2k", "ftp", "http", "https", "irc",
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"mailto", "news", "gopher", "nntp", "telnet", "webcal",
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"xmpp", "callto", "feed", "urn", "aim", "rsync", "tag",
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"ssh", "sftp", "rtsp", "afs" ]
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mathml_attributes :: [Text]
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mathml_attributes = ["actiontype", "align", "columnalign", "columnalign",
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"columnalign", "columnlines", "columnspacing", "columnspan", "depth",
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"display", "displaystyle", "equalcolumns", "equalrows", "fence",
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"fontstyle", "fontweight", "frame", "height", "linethickness", "lspace",
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"mathbackground", "mathcolor", "mathvariant", "mathvariant", "maxsize",
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"minsize", "other", "rowalign", "rowalign", "rowalign", "rowlines",
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"rowspacing", "rowspan", "rspace", "scriptlevel", "selection",
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"separator", "stretchy", "width", "width", "xlink:href", "xlink:show",
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"xlink:type", "xmlns", "xmlns:xlink"]
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svg_attributes :: [Text]
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svg_attributes = ["accent-height", "accumulate", "additive", "alphabetic",
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"arabic-form", "ascent", "attributeName", "attributeType",
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"baseProfile", "bbox", "begin", "by", "calcMode", "cap-height",
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"class", "clip-path", "color", "color-rendering", "content", "cx",
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"cy", "d", "dx", "dy", "descent", "display", "dur", "end", "fill",
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"fill-opacity", "fill-rule", "font-family", "font-size",
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"font-stretch", "font-style", "font-variant", "font-weight", "from",
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"fx", "fy", "g1", "g2", "glyph-name", "gradientUnits", "hanging",
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"height", "horiz-adv-x", "horiz-origin-x", "id", "ideographic", "k",
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"keyPoints", "keySplines", "keyTimes", "lang", "marker-end",
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"marker-mid", "marker-start", "markerHeight", "markerUnits",
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"markerWidth", "mathematical", "max", "min", "name", "offset",
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"opacity", "orient", "origin", "overline-position",
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"overline-thickness", "panose-1", "path", "pathLength", "points",
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"preserveAspectRatio", "r", "refX", "refY", "repeatCount",
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"repeatDur", "requiredExtensions", "requiredFeatures", "restart",
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"rotate", "rx", "ry", "slope", "stemh", "stemv", "stop-color",
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"stop-opacity", "strikethrough-position", "strikethrough-thickness",
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"stroke", "stroke-dasharray", "stroke-dashoffset", "stroke-linecap",
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"stroke-linejoin", "stroke-miterlimit", "stroke-opacity",
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"stroke-width", "systemLanguage", "target", "text-anchor", "to",
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"transform", "type", "u1", "u2", "underline-position",
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"underline-thickness", "unicode", "unicode-range", "units-per-em",
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"values", "version", "viewBox", "visibility", "width", "widths", "x",
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"x-height", "x1", "x2", "xlink:actuate", "xlink:arcrole",
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"xlink:href", "xlink:role", "xlink:show", "xlink:title", "xlink:type",
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"xml:base", "xml:lang", "xml:space", "xmlns", "xmlns:xlink", "y",
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"y1", "y2", "zoomAndPan"]
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-- the values for these need to be escaped
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svg_attr_val_allows_ref :: [Text]
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svg_attr_val_allows_ref = ["clip-path", "color-profile", "cursor", "fill",
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"filter", "marker", "marker-start", "marker-mid", "marker-end",
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"mask", "stroke"]
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svg_allow_local_href :: [Text]
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svg_allow_local_href = ["altGlyph", "animate", "animateColor",
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"animateMotion", "animateTransform", "cursor", "feImage", "filter",
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"linearGradient", "pattern", "radialGradient", "textpath", "tref",
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"set", "use"]
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