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StripScripts(3)	      User Contributed Perl Documentation      StripScripts(3)

NAME
       HTML::StripScripts - Strip scripting constructs out of HTML

SYNOPSIS
	 use HTML::StripScripts;

	 my $hss = HTML::StripScripts->new({ Context => 'Inline' });

	 $hss->input_start_document;

	 $hss->input_start('<i>');
	 $hss->input_text('hello, world!');
	 $hss->input_end('</i>');

	 $hss->input_end_document;

	 print $hss->filtered_document;

DESCRIPTION
       This module strips scripting constructs out of HTML, leaving as much
       non-scripting markup in place as possible.  This allows web
       applications to display HTML originating from an untrusted source
       without introducing XSS (cross site scripting) vulnerabilities.

       You will probably use HTML::StripScripts::Parser rather than using this
       module directly.

       The process is based on whitelists of tags, attributes and attribute
       values.	This approach is the most secure against disguised scripting
       constructs hidden in malicious HTML documents.

       As well as removing scripting constructs, this module ensures that
       there is a matching end for each start tag, and that the tags are
       properly nested.

       Previously, in order to customise the output, you needed to subclass
       "HTML::StripScripts" and override methods.  Now, most customisation can
       be done through the "Rules" option provided to "new()". (See
       examples/declaration/ and examples/tags/ for cases where subclassing is
       necessary.)

       The HTML document must be parsed into start tags, end tags and text
       before it can be filtered by this module.  Use either
       HTML::StripScripts::Parser or HTML::StripScripts::Regex instead if you
       want to input an unparsed HTML document.

       See examples/direct/ for an example of how to feed tokens directly to
	HTML::StripScripts.

CONSTRUCTORS
       new ( CONFIG )
	   Creates a new "HTML::StripScripts" filter object, bound to a
	   particular filtering policy.	 If present, the CONFIG parameter must
	   be a hashref.  The following keys are recognized (unrecognized keys
	   will be silently ignored).

	       $s = HTML::Stripscripts->new({
		   Context	   => 'Document|Flow|Inline|NoTags',
		   BanList	   => [qw( br img )] | {br => '1', img => '1'},
		   BanAllBut	   => [qw(p div span)],
		   AllowSrc	   => 0|1,
		   AllowHref	   => 0|1,
		   AllowRelURL	   => 0|1,
		   AllowMailto	   => 0|1,
		   EscapeFiltered  => 0|1,
		   Rules	   => { See below for details },
	       });

	   "Context"
	       A string specifying the context in which the filtered document
	       will be used.  This influences the set of tags that will be
	       allowed.

	       If present, the "Context" value must be one of:

	       "Document"
		   If "Context" is "Document" then the filter will allow a
		   full HTML document, including the "HTML" tag and "HEAD" and
		   "BODY" sections.

	       "Flow"
		   If "Context" is "Flow" then most of the cosmetic tags that
		   one would expect to find in a document body are allowed,
		   including lists and tables but not including forms.

	       "Inline"
		   If "Context" is "Inline" then only inline tags such as "B"
		   and "FONT" are allowed.

	       "NoTags"
		   If "Context" is "NoTags" then no tags are allowed.

	       The default "Context" value is "Flow".

	   "BanList"
	       If present, this option must be an arrayref or a hashref.  Any
	       tag that would normally be allowed (because it presents no XSS
	       hazard) will be blocked if the lowercase name of the tag is in
	       this list.

	       For example, in a guestbook application where "HR" tags are
	       used to separate posts, you may wish to prevent posts from
	       including "HR" tags, even though "HR" is not an XSS risk.

	   "BanAllBut"
	       If present, this option must be reference to an array holding a
	       list of lowercase tag names.  This has the effect of adding all
	       but the listed tags to the ban list, so that only those tags
	       listed will be allowed.

	   "AllowSrc"
	       By default, the filter won't allow constructs that cause the
	       browser to fetch things automatically, such as "SRC" attributes
	       in "IMG" tags.  If this option is present and true then those
	       constructs will be allowed.

	   "AllowHref"
	       By default, the filter won't allow constructs that cause the
	       browser to fetch things if the user clicks on something, such
	       as the "HREF" attribute in "A" tags.  Set this option to a true
	       value to allow this type of construct.

	   "AllowRelURL"
	       By default, the filter won't allow relative URLs such as
	       "../foo.html" in "SRC" and "HREF" attribute values.  Set this
	       option to a true value to allow them. "AllowHref" and / or
	       "AllowSrc" also need to be set to true for this to have any
	       effect.

	   "AllowMailto"
	       By default, "mailto:" links are not allowed. If "AllowMailto"
	       is set to a true value, then this construct will be allowed.
	       This can be enabled separately from AllowHref.

	   "EscapeFiltered"
	       By default, any filtered tags are outputted as
	       "<!--filtered-->". If "EscapeFiltered" is set to a true value,
	       then the filtered tags are converted to HTML entities.

	       For instance:

		 <br>  -->  <br>

	   "Rules"
	       The "Rules" option provides a very flexible way of customising
	       the filter.

	       The focus is safety-first, so it is applied after all of the
	       previous validation.  This means that you cannot all malicious
	       data should already have been cleared.

	       Rules can be specified for tags and for attributes. Any tag or
	       attribute not explicitly listed will be handled by the default
	       "*" rules.

	       The following is a synopsis of all of the options that you can
	       use to configure rules.	Below, an example is broken into
	       sections and explained.

		Rules => {

		    tag => 0 | 1 | sub { tag_callback }
			   | {
			       attr	 => 0 | 1 | 'regex' | qr/regex/ | sub { attr_callback},
			       '*'	 => 0 | 1 | 'regex' | qr/regex/ | sub { attr_callback},
			       required	 => [qw(attrname attrname)],
			       tag	 => sub { tag_callback }
			     },

		   '*' => 0 | 1 | sub { tag_callback }
			  | {
			      attr => 0 | 1 | 'regex' | qr/regex/ | sub { attr_callback},
			      '*'  => 0 | 1 | 'regex' | qr/regex/ | sub { attr_callback},
			      tag  => sub { tag_callback }
			    }

		   }

	       EXAMPLE:

		   Rules => {

		       ##########################
		       ##### EXPLICIT RULES #####
		       ##########################

		       ## Allow <br> tags, reject <img> tags
		       br	   => 1,
		       img	   => 0,

		       ## Send all <div> tags to a sub
		       div	   => sub { tag_callback },

		       ## Allow <blockquote> tags,and allow the 'cite' attribute
		       ## All other attributes are handled by the default C<*>
		       blockquote  => {
			   cite	   => 1,
		       },

		       ## Allow <a> tags, and
		       a  => {

			   ## Allow the 'title' attribute
			   title     => 1,

			   ## Allow the 'href' attribute if it matches the regex
			   href	   =>	'^http://yourdomain.com'
		      OR   href	   => qr{^http://yourdomain.com},

			   ## 'style' attributes are handled by a sub
			   style     => sub { attr_callback },

			   ## All other attributes are rejected
			   '*'	     => 0,

			   ## Additionally, the <a> tag should be handled by this sub
			   tag	     => sub { tag_callback},

			   ## If the <a> tag doesn't have these attributes, filter the tag
			   required  => [qw(href title)],

		       },

		       ##########################
		       ##### DEFAULT RULES #####
		       ##########################

		       ## The default '*' rule - accepts all the same options as above.
		       ## If a tag or attribute is not mentioned above, then the default
		       ## rule is applied:

		       ## Reject all tags
		       '*'	   => 0,

		       ## Allow all tags and all attributes
		       '*'	   => 1,

		       ## Send all tags to the sub
		       '*'	   => sub { tag_callback },

		       ## Allow all tags, reject all attributes
		       '*'	   => { '*'  => 0 },

		       ## Allow all tags, and
		       '*' => {

			   ## Allow the 'title' attribute
			   title   => 1,

			   ## Allow the 'href' attribute if it matches the regex
			   href	   =>	'^http://yourdomain.com'
		      OR   href	   => qr{^http://yourdomain.com},

			   ## 'style' attributes are handled by a sub
			   style   => sub { attr_callback },

			   ## All other attributes are rejected
			   '*'	   => 0,

			   ## Additionally, all tags should be handled by this sub
			   tag	   => sub { tag_callback},

		       },

	       Tag Callbacks
		       sub tag_callback {
			   my ($filter,$element) = (@_);

			   $element = {
			       tag	=> 'tag',
			       content	=> 'inner_html',
			       attr	=> {
				   attr_name => 'attr_value',
			       }
			   };
			   return 0 | 1;
		       }

		   A tag callback accepts two parameters, the $filter object
		   and the C$element>.	It should return 0 to completely
		   ignore the tag and its content (which includes any nested
		   HTML tags), or 1 to accept and output the tag.

		   The $element is a hash ref containing the keys:

	       "tag"
		   This is the tagname in lowercase, eg "a", "br", "img". If
		   you set the tag value to an empty string, then the tag will
		   not be outputted, but the tag contents will.

	       "content"
		   This is the equivalent of DOM's innerHTML. It contains the
		   text content and any HTML tags contained within this
		   element. You can change the content or set it to an empty
		   string so that it is not outputted.

	       "attr"
		   "attr" contains a hashref containing the attribute names
		   and values

	       If for instance, you wanted to replace "<b>" tags with "<span>"
	       tags, you could do this:

		   sub b_callback {
		       my ($filter,$element)   = @_;
		       $element->{tag}	       = 'span';
		       $element->{attr}{style} = 'font-weight:bold';
		       return 1;
		   }

	   Attribute Callbacks
		   sub attr_callback {
		       my ( $filter, $tag, $attr_name, $attr_val ) = @_;
		       return undef | '' | 'value';
		   }

	       Attribute callbacks accept four parameters, the $filter object,
	       the $tag name, the $attr_name and the $attr_value.

	       It should return either "undef" to reject the attribute, or the
	       value to be used. An empty string keeps the attribute, but
	       without a value.

	   "BanList" vs "BanAllBut" vs "Rules"
	       It is not necessary to use "BanList" or "BanAllBut" -
	       everything can be done via "Rules", however it may be simpler
	       to write:

		   BanAllBut => [qw(p div span)]

	       The logic works as follows:

		  * If BanAllBut exists, then ban everything but the tags in the list
		  * Add to the ban list any elements in BanList
		  * Any tags mentioned explicitly in Rules (eg a => 0, br => 1)
		    are added or removed from the BanList
		  * A default rule of { '*' => 0 } would ban all tags except
		    those mentioned in Rules
		  * A default rule of { '*' => 1 } would allow all tags except
		    those disallowed in the ban list, or by explicit rules

METHODS
       This class provides the following methods:

       hss_init ()
	   This method is called by new() and does the actual initialisation
	   work for the new HTML::StripScripts object.

       input_start_document ()
	   This method initializes the filter, and must be called once before
	   starting on each HTML document to be filtered.

       input_start ( TEXT )
	   Handles a start tag from the input document.	 TEXT must be the full
	   text of the tag, including angle-brackets.

       input_end ( TEXT )
	   Handles an end tag from the input document.	TEXT must be the full
	   text of the end tag, including angle-brackets.

       input_text ( TEXT )
	   Handles some non-tag text from the input document.

       input_process ( TEXT )
	   Handles a processing instruction from the input document.

       input_comment ( TEXT )
	   Handles an HTML comment from the input document.

       input_declaration ( TEXT )
	   Handles an declaration from the input document.

       input_end_document ()
	   Call this method to signal the end of the input document.

       filtered_document ()
	   Returns the filtered document as a string.

SUBCLASSING
       The only reason for subclassing this module now is to add to the list
       of accepted tags, attributes and styles (See "WHITELIST INITIALIZATION
       METHODS").  Everything else can be achieved with "Rules".

       The "HTML::StripScripts" class is subclassable.	Filter objects are
       plain hashes and "HTML::StripScripts" reserves only hash keys that
       start with "_hss".  The filter configuration can be set up by invoking
       the hss_init() method, which takes the same arguments as new().

OUTPUT METHODS
       The filter outputs a stream of start tags, end tags, text, comments,
       declarations and processing instructions, via the following "output_*"
       methods.	 Subclasses may override these to intercept the filter output.

       The default implementations of the "output_*" methods pass the text on
       to the output() method.	The default implementation of the output()
       method appends the text to a string, which can be fetched with the
       filtered_document() method once processing is complete.

       If the output() method or the individual "output_*" methods are
       overridden in a subclass, then filtered_document() will not work in
       that subclass.

       output_start_document ()
	   This method gets called once at the start of each HTML document
	   passed through the filter.  The default implementation does
	   nothing.

       output_end_document ()
	   This method gets called once at the end of each HTML document
	   passed through the filter.  The default implementation does
	   nothing.

       output_start ( TEXT )
	   This method is used to output a filtered start tag.

       output_end ( TEXT )
	   This method is used to output a filtered end tag.

       output_text ( TEXT )
	   This method is used to output some filtered non-tag text.

       output_declaration ( TEXT )
	   This method is used to output a filtered declaration.

       output_comment ( TEXT )
	   This method is used to output a filtered HTML comment.

       output_process ( TEXT )
	   This method is used to output a filtered processing instruction.

       output ( TEXT )
	   This method is invoked by all of the default "output_*" methods.
	   The default implementation appends the text to the string that the
	   filtered_document() method will return.

       output_stack_entry ( TEXT )
	   This method is invoked when a tag plus all text and nested HTML
	   content within the tag has been processed. It adds the tag plus its
	   content to the content for its parent tag.

REJECT METHODS
       When the filter encounters something in the input document which it
       cannot transform into an acceptable construct, it invokes one of the
       following "reject_*" methods to put something in the output document to
       take the place of the unacceptable construct.

       The TEXT parameter is the full text of the unacceptable construct.

       The default implementations of these methods output an HTML comment
       containing the text "filtered". If "EscapeFiltered" is set to true,
       then the rejected text is HTML escaped instead.

       Subclasses may override these methods, but should exercise caution.
       The TEXT parameter is unfiltered input and may contain malicious
       constructs.

       reject_start ( TEXT )
       reject_end ( TEXT )
       reject_text ( TEXT )
       reject_declaration ( TEXT )
       reject_comment ( TEXT )
       reject_process ( TEXT )

WHITELIST INITIALIZATION METHODS
       The filter refers to various whitelists to determine which constructs
       are acceptable.	To modify these whitelists, subclasses can override
       the following methods.

       Each method is called once at object initialization time, and must
       return a reference to a nested data structure.  These references are
       installed into the object, and used whenever the filter needs to refer
       to a whitelist.

       The default implementations of these methods can be invoked as class
       methods.

       See examples/tags/ and examples/declaration/ for examples of how to
       override these methods.

       init_context_whitelist ()
	   Returns a reference to the "Context" whitelist, which determines
	   which tags may appear at each point in the document, and which
	   other tags may be nested within them.

	   It is a hash, and the keys are context names, such as "Flow" and
	   "Inline".

	   The values in the hash are hashrefs.	 The keys in these subhashes
	   are lowercase tag names, and the values are context names,
	   specifying the context that the tag provides to any other tags
	   nested within it.

	   The special context "EMPTY" as a value in a subhash indicates that
	   nothing can be nested within that tag.

       init_attrib_whitelist ()
	   Returns a reference to the "Attrib" whitelist, which determines
	   which attributes each tag can have and the values that those
	   attributes can take.

	   It is a hash, and the keys are lowercase tag names.

	   The values in the hash are hashrefs.	 The keys in these subhashes
	   are lowercase attribute names, and the values are attribute value
	   class names, which are short strings describing the type of values
	   that the attribute can take, such as "color" or "number".

       init_attval_whitelist ()
	   Returns a reference to the "AttVal" whitelist, which is a hash that
	   maps attribute value class names from the "Attrib" whitelist to
	   coderefs to subs to validate (and optionally transform) a
	   particular attribute value.

	   The filter calls the attribute value validation subs with the
	   following parameters:

	   "filter"
	       A reference to the filter object.

	   "tagname"
	       The lowercase name of the tag in which the attribute appears.

	   "attrname"
	       The name of the attribute.

	   "attrval"
	       The attribute value found in the input document, in canonical
	       form (see "CANONICAL FORM").

	   The validation sub can return undef to indicate that the attribute
	   should be removed from the tag, or it can return the new value for
	   the attribute, in canonical form.

       init_style_whitelist ()
	   Returns a reference to the "Style" whitelist, which determines
	   which CSS style directives are permitted in "style" tag attributes.
	   The keys are value names such as "color" and "background-color",
	   and the values are class names to be used as keys into the "AttVal"
	   whitelist.

       init_deinter_whitelist
	   Returns a reference to the "DeInter" whitelist, which determines
	   which inline tags the filter should attempt to automatically de-
	   interleave if they are encountered interleaved.  For example, the
	   filter will transform:

	     <b>hello <i>world</b> !</i>

	   Into:

	     <b>hello <i>world</i></b><i> !</i>

	   because both "b" and "i" appear as keys in the "DeInter" whitelist.

CHARACTER DATA PROCESSING
       These methods transform attribute values and non-tag text from the
       input document into canonical form (see "CANONICAL FORM"), and
       transform text in canonical form into a suitable form for the output
       document.

       text_to_canonical_form ( TEXT )
	   This method is used to reduce non-tag text from the input document
	   to canonical form before passing it to the filter_text() method.

	   The default implementation unescapes all entities that map to
	   "US-ASCII" characters other than ampersand, and replaces any
	   ampersands that don't form part of valid entities with "&".

       quoted_to_canonical_form ( VALUE )
	   This method is used to reduce attribute values quoted with
	   doublequotes or singlequotes to canonical form before passing it to
	   the handler subs in the "AttVal" whitelist.

	   The default behavior is the same as that of
	   "text_to_canonical_form()", plus it converts any CR, LF or TAB
	   characters to spaces.

       unquoted_to_canonical_form ( VALUE )
	   This method is used to reduce attribute values without quotes to
	   canonical form before passing it to the handler subs in the
	   "AttVal" whitelist.

	   The default implementation simply replaces all ampersands with
	   "&", since that corresponds with the way most browsers treat
	   entities in unquoted values.

       canonical_form_to_text ( TEXT )
	   This method is used to convert the text in canonical form returned
	   by the filter_text() method to a form suitable for inclusion in the
	   output document.

	   The default implementation runs anything that doesn't look like a
	   valid entity through the escape_html_metachars() method.

       canonical_form_to_attval ( ATTVAL )
	   This method is used to convert the text in canonical form returned
	   by the "AttVal" handler subs to a form suitable for inclusion in
	   doublequotes in the output tag.

	   The default implementation converts CR, LF and TAB characters to a
	   single space, and runs anything that doesn't look like a valid
	   entity through the escape_html_metachars() method.

       validate_href_attribute ( TEXT )
	   If the "AllowHref" filter configuration option is set, then this
	   method is used to validate "href" type attribute values.  TEXT is
	   the attribute value in canonical form.  Returns a possibly modified
	   attribute value (in canonical form) or "undef" to reject the
	   attribute.

	   The default implementation allows only absolute "http" and "https"
	   URLs, permits port numbers and query strings, and imposes
	   reasonable length limits.

	   It does not URI escape the query string, and it does not guarantee
	   properly formatted URIs, it just tries to give safe URIs. You can
	   always use an attribute callback (see "Attribute Callbacks") to
	   provide stricter handling.

       validate_mailto ( TEXT )
	   If the "AllowMailto" filter configuration option is set, then this
	   method is used to validate "href" type attribute values which begin
	   with "mailto:".  TEXT is the attribute value in canonical form.
	   Returns a possibly modified attribute value (in canonical form) or
	   "undef" to reject the attribute.

	   This uses a lightweight regex and does not guarantee that email
	   addresses are properly formatted. You can always use an attribute
	   callback (see "Attribute Callbacks") to provide stricter handling.

       validate_src_attribute ( TEXT )
	   If the "AllowSrc" filter configuration option is set, then this
	   method is used to validate "src" type attribute values.  TEXT is
	   the attribute value in canonical form.  Returns a possibly modified
	   attribute value (in canonical form) or "undef" to reject the
	   attribute.

	   The default implementation behaves as validate_href_attribute().

OTHER METHODS TO OVERRIDE
       As well as the output, reject, init and cdata methods listed above, it
       might make sense for subclasses to override the following methods:

       filter_text ( TEXT )
	   This method will be invoked to filter blocks of non-tag text in the
	   input document.  Both input and output are in canonical form, see
	   "CANONICAL FORM".

	   The default implementation does no filtering.

       escape_html_metachars ( TEXT )
	   This method is used to escape all HTML metacharacters in TEXT.  The
	   return value must be a copy of TEXT with metacharacters escaped.

	   The default implementation escapes a minimal set of metacharacters
	   for security against XSS vulnerabilities.  The set of characters to
	   escape is a compromise between the need for security and the need
	   to ensure that the filter will work for documents in as many
	   different character sets as possible.

	   Subclasses which make strong assumptions about the document
	   character set will be able to escape much more aggressively.

       strip_nonprintable ( TEXT )
	   Returns a copy of TEXT with runs of nonprintable characters
	   replaced with spaces or some other harmless string.	Avoids
	   replacing anything with the empty string, as that can lead to other
	   security issues.

	   The default implementation strips out only NULL characters, in
	   order to avoid scrambling text for as many different character sets
	   as possible.

	   Subclasses which make some sort of assumption about the character
	   set in use will be able to have a much wider definition of a
	   nonprintable character, and hence a more secure
	   strip_nonprintable() implementation.

ATTRIBUTE VALUE HANDLER SUBS
       References to the following subs appear in the "AttVal" whitelist
       returned by the init_attval_whitelist() method.

       _hss_attval_style( FILTER, TAGNAME, ATTRNAME, ATTRVAL )
	   Attribute value hander for the "style" attribute.

       _hss_attval_size ( FILTER, TAGNAME, ATTRNAME, ATTRVAL )
	   Attribute value handler for attributes who's values are some sort
	   of size or length.

       _hss_attval_number ( FILTER, TAGNAME, ATTRNAME, ATTRVAL )
	   Attribute value handler for attributes who's values are a simple
	   integer.

       _hss_attval_color ( FILTER, TAGNAME, ATTRNAME, ATTRVAL )
	   Attribute value handler for color attributes.

       _hss_attval_text ( FILTER, TAGNAME, ATTRNAME, ATTRVAL )
	   Attribute value handler for text attributes.

       _hss_attval_word ( FILTER, TAGNAME, ATTRNAME, ATTRVAL )
	   Attribute value handler for attributes who's values must consist of
	   a single short word, with minus characters permitted.

       _hss_attval_wordlist ( FILTER, TAGNAME, ATTRNAME, ATTRVAL )
	   Attribute value handler for attributes who's values must consist of
	   one or more words, separated by spaces and/or commas.

       _hss_attval_wordlistq ( FILTER, TAGNAME, ATTRNAME, ATTRVAL )
	   Attribute value handler for attributes who's values must consist of
	   one or more words, separated by commas, with optional doublequotes
	   around words and spaces allowed within the doublequotes.

       _hss_attval_href ( FILTER, TAGNAME, ATTRNAME, ATTRVAL )
	   Attribute value handler for "href" type attributes.	If the
	   "AllowHref" or "AllowMailto" configuration options are set, uses
	   the validate_href_attribute() method to check the attribute value.

       _hss_attval_src ( FILTER, TAGNAME, ATTRNAME, ATTRVAL )
	   Attribute value handler for "src" type attributes.  If the
	   "AllowSrc" configuration option is set, uses the
	   validate_src_attribute() method to check the attribute value.

       _hss_attval_stylesrc ( FILTER, TAGNAME, ATTRNAME, ATTRVAL )
	   Attribute value handler for "src" type style pseudo attributes.

       _hss_attval_novalue ( FILTER, TAGNAME, ATTRNAME, ATTRVAL )
	   Attribute value handler for attributes that have no value or a
	   value that is ignored.  Just returns the attribute name as the
	   value.

CANONICAL FORM
       Many of the methods described above deal with text from the input
       document, encoded in what I call "canonical form", defined as follows:

       All characters other than ampersands represent themselves.  Literal
       ampersands are encoded as "&".  Non "US-ASCII" characters may
       appear as literals in whatever character set is in use, or they may
       appear as named or numeric HTML entities such as "æ", "穩"
       and "ÿ".  Unknown named entities such as "&foo;" may appear.

       The idea is to be able to be able to reduce input text to a minimal
       form, without making too many assumptions about the character set in
       use.

PRIVATE METHODS
       The following methods are internal to this class, and should not be
       invoked from elsewhere.	Subclasses should not use or override these
       methods.

       _hss_prepare_ban_list (CFG)
	   Returns a hash ref representing all the banned tags, based on the
	   values of BanList and BanAllBut

       _hss_prepare_rules (CFG)
	   Returns a hash ref representing the tag and attribute rules (See
	   "Rules").

	   Returns undef if no filters are specified, in which case the
	   attribute filter code has very little performance impact. If any
	   rules are specified, then every tag and attribute is checked.

       _hss_get_attr_filter ( DEFAULT_FILTERS TAG_FILTERS ATTR_NAME)
	   Returns the attribute filter rule to apply to this particular
	   attribute.

	   Checks for:

	     - a named attribute rule in a named tag
	     - a default * attribute rule in a named tag
	     - a named attribute rule in the default * rules
	     - a default * attribute rule in the default * rules

       _hss_join_attribs (FILTERED_ATTRIBS)
	   Accepts a hash ref containing the attribute names as the keys, and
	   the attribute values as the values.	Escapes them and returns a
	   string ready for output to HTML

       _hss_decode_numeric ( NUMERIC )
	   Returns the string that should replace the numeric entity NUMERIC
	   in the text_to_canonical_form() method.

       _hss_tag_is_banned ( TAGNAME )
	   Returns true if the lower case tag name TAGNAME is on the list of
	   harmless tags that the filter is configured to block, false
	   otherwise.

       _hss_get_to_valid_context ( TAG )
	   Tries to get the filter to a context in which the tag TAG is
	   allowed, by introducing extra end tags or start tags if necessary.
	   TAG can be either the lower case name of a tag or the string
	   'CDATA'.

	   Returns 1 if an allowed context is reached, or 0 if there's no
	   reasonable way to get to an allowed context and the tag should just
	   be rejected.

       _hss_close_innermost_tag ()
	   Closes the innermost open tag.

       _hss_context ()
	   Returns the current named context of the filter.

       _hss_valid_in_context ( TAG, CONTEXT )
	   Returns true if the lowercase tag name TAG is valid in context
	   CONTEXT, false otherwise.

       _hss_valid_in_current_context ( TAG )
	   Returns true if the lowercase tag name TAG is valid in the filter's
	   current context, false otherwise.

BUGS AND LIMITATIONS
       Performance
	   This module does a lot of work to ensure that tags are correctly
	   nested and are not left open, causing unnecessary overhead for
	   applications where that doesn't matter.

	   Such applications may benefit from using the more lightweight
	   HTML::Scrubber::StripScripts module instead.

       Strictness
	   URIs and email addresses are cleaned up to be safe, but not
	   necessarily accurate.  That would have required adding
	   dependencies.  Attribute callbacks can be used to add this
	   functionality if required, or the validation methods can be
	   overriden.

	   By default, filtered HTML may not be valid strict XHTML, for
	   instance empty required attributes may be outputted.	 However, with
	   "Rules", it should be possible to force the HTML to validate.

       REPORTING BUGS
	   Please report any bugs or feature requests to
	   bug-html-stripscripts@rt.cpan.org, or through the web interface at
	   <http://rt.cpan.org>.

SEE ALSO
       HTML::Parser, HTML::StripScripts::Parser, HTML::StripScripts::Regex

AUTHOR
       Original author Nick Cleaton <nick@cleaton.net>

       New code added and module maintained by Clinton Gormley
       <clint@traveljury.com>

COPYRIGHT
       Copyright (C) 2003 Nick Cleaton.	 All Rights Reserved.

       Copyright (C) 2007 Clinton Gormley.  All Rights Reserved.

LICENSE
       This module is free software; you can redistribute it and/or modify it
       under the same terms as Perl itself.

perl v5.14.1			  2009-11-05		       StripScripts(3)
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