htmlpurifier/docs/proposal-new-directives.txt

Configuration Ideas

Here are some theoretical configuration ideas that we could implement some
time.  Note the naming convention: %Namespace.Directive. If you want one
implemented, give us a ring, and we'll move it up the priority chain.

%Attr.RewriteFragments - if there's %Attr.IDPrefix we may want to transparently
    rewrite the URLs we parse too.  However, we can only do it when it's a pure
    anchor link, so it's not foolproof

%Attr.ClassBlacklist,
%Attr.ClassWhitelist,
%Attr.ClassPolicy - determines what classes are allowed. When
    %Attr.ClassPolicy is set to Blacklist, only allow those not in
    %Attr.ClassBlacklist. When it's Whitelist, only allow those in
    %Attr.ClassWhitelist.

%Attr.MaxWidth, 
%Attr.MaxHeight - caps for width and height related checks.
    (the hack in Pixels for an image crashing attack could be replaced by this)

%URI.AddRelNofollow - will add rel="nofollow" to all links, preventing the
    spread of ill-gotten pagerank

%URI.HostBlacklistRegex - regexes that if matching the host are disallowed
%URI.HostWhitelist - domain names that are excluded from the host blacklist
%URI.HostPolicy - determines whether or not its reject all and then whitelist
    or allow all in then do specific blacklists with whitelist intervening.
    'DenyAll' or 'AllowAll' (default)

%URI.DisableIPHosts - URIs that have IP addresses for hosts are disallowed.
    Be sure to also grab unusual encodings (dword, hex and octal), which may
    be currently be caught by regular DNS
%URI.DisableIDN - Disallow raw internationalized domain names. Punycode
    will still be permitted.

%URI.ConvertUnusualIPHosts - transform dword/hex/octal IP addresses to the
    regular form
%URI.ConvertAbsoluteDNS - Remove extra dots after host names that trigger
    absolute DNS.  While this is actually the preferred method according to
    the RFC, most people opt to use a relative domain name relative to . (root).