HTML::Element(3pm) User Contributed Perl Documentation HTML::Element(3pm) NAME HTML::Element - Class for objects that represent HTML elements VERSION This document describes version 5.07 of HTML::Element, released August 31, 2017 as part of HTML-Tree. SYNOPSIS use HTML::Element; $a = HTML::Element->new('a', href => 'http://www.perl.com/'); $a->push_content("The Perl Homepage"); $tag = $a->tag; print "$tag starts out as:", $a->starttag, "\n"; print "$tag ends as:", $a->endtag, "\n"; print "$tag\'s href attribute is: ", $a->attr('href'), "\n"; $links_r = $a->extract_links(); print "Hey, I found ", scalar(@$links_r), " links.\n"; print "And that, as HTML, is: ", $a->as_HTML, "\n"; $a = $a->delete; DESCRIPTION (This class is part of the HTML::Tree dist.) Objects of the HTML::Element class can be used to represent elements of HTML document trees. These objects have attributes, notably attributes that designates each element's parent and content. The content is an array of text segments and other HTML::Element objects. A tree with HTML::Element objects as nodes can represent the syntax tree for a HTML document. HOW WE REPRESENT TREES Consider this HTML document: Stuff

I like potatoes!

Building a syntax tree out of it makes a tree-structure in memory that could be diagrammed as: html (lang='en-US') / \ / \ / \ head body /\ \ / \ \ / \ \ title meta h1 | (name='author', | "Stuff" content='Jojo') "I like potatoes" This is the traditional way to diagram a tree, with the "root" at the top, and it's this kind of diagram that people have in mind when they say, for example, that "the meta element is under the head element instead of under the body element". (The same is also said with "inside" instead of "under" -- the use of "inside" makes more sense when you're looking at the HTML source.) Another way to represent the above tree is with indenting: html (attributes: lang='en-US') head title "Stuff" meta (attributes: name='author' content='Jojo') body h1 "I like potatoes" Incidentally, diagramming with indenting works much better for very large trees, and is easier for a program to generate. The "$tree->dump" method uses indentation just that way. However you diagram the tree, it's stored the same in memory -- it's a network of objects, each of which has attributes like so: element #1: _tag: 'html' _parent: none _content: [element #2, element #5] lang: 'en-US' element #2: _tag: 'head' _parent: element #1 _content: [element #3, element #4] element #3: _tag: 'title' _parent: element #2 _content: [text segment "Stuff"] element #4 _tag: 'meta' _parent: element #2 _content: none name: author content: Jojo element #5 _tag: 'body' _parent: element #1 _content: [element #6] element #6 _tag: 'h1' _parent: element #5 _content: [text segment "I like potatoes"] The "treeness" of the tree-structure that these elements comprise is not an aspect of any particular object, but is emergent from the relatedness attributes (_parent and _content) of these element-objects and from how you use them to get from element to element. While you could access the content of a tree by writing code that says "access the 'src' attribute of the root's first child's seventh child's third child", you're more likely to have to scan the contents of a tree, looking for whatever nodes, or kinds of nodes, you want to do something with. The most straightforward way to look over a tree is to "traverse" it; an HTML::Element method ("$h->traverse") is provided for this purpose; and several other HTML::Element methods are based on it. (For everything you ever wanted to know about trees, and then some, see Niklaus Wirth's Algorithms + Data Structures = Programs or Donald Knuth's The Art of Computer Programming, Volume 1.) Weak References TL;DR summary: "use HTML::TreeBuilder 5 -weak;" and forget about the "delete" method (except for pruning a node from a tree). Because HTML::Element stores a reference to the parent element, Perl's reference-count garbage collection doesn't work properly with HTML::Element trees. Starting with version 5.00, HTML::Element uses weak references (if available) to prevent that problem. Weak references were introduced in Perl 5.6.0, but you also need a version of Scalar::Util that provides the "weaken" function. Weak references are enabled by default. If you want to be certain they're in use, you can say "use HTML::Element 5 -weak;". You must include the version number; previous versions of HTML::Element ignored the import list entirely. To disable weak references, you can say "use HTML::Element -noweak;". This is a global setting. This feature is deprecated and is provided only as a quick fix for broken code. If your code does not work properly with weak references, you should fix it immediately, as weak references may become mandatory in a future version. Generally, all you need to do is keep a reference to the root of the tree until you're done working with it. Because HTML::TreeBuilder is a subclass of HTML::Element, you can also import "-weak" or "-noweak" from HTML::TreeBuilder: e.g. "use HTML::TreeBuilder: 5 -weak;". BASIC METHODS new $h = HTML::Element->new('tag', 'attrname' => 'value', ... ); This constructor method returns a new HTML::Element object. The tag name is a required argument; it will be forced to lowercase. Optionally, you can specify other initial attributes at object creation time. attr $value = $h->attr('attr'); $old_value = $h->attr('attr', $new_value); Returns (optionally sets) the value of the given attribute of $h. The attribute name (but not the value, if provided) is forced to lowercase. If trying to read the value of an attribute not present for this element, the return value is undef. If setting a new value, the old value of that attribute is returned. If methods are provided for accessing an attribute (like "$h->tag" for "_tag", "$h->content_list", etc. below), use those instead of calling attr "$h->attr", whether for reading or setting. Note that setting an attribute to "undef" (as opposed to "", the empty string) actually deletes the attribute. tag $tagname = $h->tag(); $h->tag('tagname'); Returns (optionally sets) the tag name (also known as the generic identifier) for the element $h. In setting, the tag name is always converted to lower case. There are four kinds of "pseudo-elements" that show up as HTML::Element objects: Comment pseudo-elements These are element objects with a "$h->tag" value of "~comment", and the content of the comment is stored in the "text" attribute ("$h->attr("text")"). For example, parsing this code with HTML::TreeBuilder... produces an HTML::Element object with these attributes: "_tag", "~comment", "text", " I like Pie.\n Pie is good\n " Declaration pseudo-elements Declarations (rarely encountered) are represented as HTML::Element objects with a tag name of "~declaration", and content in the "text" attribute. For example, this: produces an element whose attributes include: "_tag", "~declaration", "text", "DOCTYPE foo" Processing instruction pseudo-elements PIs (rarely encountered) are represented as HTML::Element objects with a tag name of "~pi", and content in the "text" attribute. For example, this: produces an element whose attributes include: "_tag", "~pi", "text", "stuff foo?" (assuming a recent version of HTML::Parser) ~literal pseudo-elements These objects are not currently produced by HTML::TreeBuilder, but can be used to represent a "super-literal" -- i.e., a literal you want to be immune from escaping. (Yes, I just made that term up.) That is, this is useful if you want to insert code into a tree that you plan to dump out with "as_HTML", where you want, for some reason, to suppress "as_HTML"'s normal behavior of amp-quoting text segments. For example, this: my $literal = HTML::Element->new('~literal', 'text' => 'x < 4 & y > 7' ); my $span = HTML::Element->new('span'); $span->push_content($literal); print $span->as_HTML; prints this: x < 4 & y > 7 Whereas this: my $span = HTML::Element->new('span'); $span->push_content('x < 4 & y > 7'); # normal text segment print $span->as_HTML; prints this: x < 4 & y > 7 Unless you're inserting lots of pre-cooked code into existing trees, and dumping them out again, it's not likely that you'll find "~literal" pseudo-elements useful. parent $parent = $h->parent(); $h->parent($new_parent); Returns (optionally sets) the parent (aka "container") for this element. The parent should either be undef, or should be another element. You should not use this to directly set the parent of an element. Instead use any of the other methods under "Structure-Modifying Methods", below. Note that not($h->parent) is a simple test for whether $h is the root of its subtree. content_list @content = $h->content_list(); $num_children = $h->content_list(); Returns a list of the child nodes of this element -- i.e., what nodes (elements or text segments) are inside/under this element. (Note that this may be an empty list.) In a scalar context, this returns the count of the items, as you may expect. content $content_array_ref = $h->content(); # may return undef This somewhat deprecated method returns the content of this element; but unlike content_list, this returns either undef (which you should understand to mean no content), or a reference to the array of content items, each of which is either a text segment (a string, i.e., a defined non-reference scalar value), or an HTML::Element object. Note that even if an arrayref is returned, it may be a reference to an empty array. While older code should feel free to continue to use "$h->content", new code should use "$h->content_list" in almost all conceivable cases. It is my experience that in most cases this leads to simpler code anyway, since it means one can say: @children = $h->content_list; instead of the inelegant: @children = @{$h->content || []}; If you do use "$h->content" (or "$h->content_array_ref"), you should not use the reference returned by it (assuming it returned a reference, and not undef) to directly set or change the content of an element or text segment! Instead use content_refs_list or any of the other methods under "Structure-Modifying Methods", below. content_array_ref $content_array_ref = $h->content_array_ref(); # never undef This is like "content" (with all its caveats and deprecations) except that it is guaranteed to return an array reference. That is, if the given node has no "_content" attribute, the "content" method would return that undef, but "content_array_ref" would set the given node's "_content" value to "[]" (a reference to a new, empty array), and return that. content_refs_list @content_refs = $h->content_refs_list; This returns a list of scalar references to each element of $h's content list. This is useful in case you want to in-place edit any large text segments without having to get a copy of the current value of that segment value, modify that copy, then use the "splice_content" to replace the old with the new. Instead, here you can in-place edit: foreach my $item_r ($h->content_refs_list) { next if ref $$item_r; $$item_r =~ s/honour/honor/g; } You could currently achieve the same affect with: foreach my $item (@{ $h->content_array_ref }) { # deprecated! next if ref $item; $item =~ s/honour/honor/g; } ...except that using the return value of "$h->content" or "$h->content_array_ref" to do that is deprecated, and just might stop working in the future. implicit $is_implicit = $h->implicit(); $h->implicit($make_implicit); Returns (optionally sets) the "_implicit" attribute. This attribute is a flag that's used for indicating that the element was not originally present in the source, but was added to the parse tree (by HTML::TreeBuilder, for example) in order to conform to the rules of HTML structure. pos $pos = $h->pos(); $h->pos($element); Returns (and optionally sets) the "_pos" (for "current position") pointer of $h. This attribute is a pointer used during some parsing operations, whose value is whatever HTML::Element element at or under $h is currently "open", where "$h->insert_element(NEW)" will actually insert a new element. (This has nothing to do with the Perl function called "pos", for controlling where regular expression matching starts.) If you set "$h->pos($element)", be sure that $element is either $h, or an element under $h. If you've been modifying the tree under $h and are no longer sure "$h->pos" is valid, you can enforce validity with: $h->pos(undef) unless $h->pos->is_inside($h); all_attr %attr = $h->all_attr(); Returns all this element's attributes and values, as key-value pairs. This will include any "internal" attributes (i.e., ones not present in the original element, and which will not be represented if/when you call "$h->as_HTML"). Internal attributes are distinguished by the fact that the first character of their key (not value! key!) is an underscore ("_"). Example output of "$h->all_attr()" : "'_parent', "[object_value]" , '_tag', 'em', 'lang', 'en-US', '_content', "[array-ref value]. all_attr_names @names = $h->all_attr_names(); $num_attrs = $h->all_attr_names(); Like "all_attr", but only returns the names of the attributes. In scalar context, returns the number of attributes. Example output of "$h->all_attr_names()" : "'_parent', '_tag', 'lang', '_content', ". all_external_attr %attr = $h->all_external_attr(); Like "all_attr", except that internal attributes are not present. all_external_attr_names @names = $h->all_external_attr_names(); $num_attrs = $h->all_external_attr_names(); Like "all_attr_names", except that internal attributes' names are not present (or counted). id $id = $h->id(); $h->id($string); Returns (optionally sets to $string) the "id" attribute. "$h->id(undef)" deletes the "id" attribute. "$h->id(...)" is basically equivalent to "$h->attr('id', ...)", except that when setting the attribute, this method returns the new value, not the old value. idf $id = $h->idf(); $h->idf($string); Just like the "id" method, except that if you call "$h->idf()" and no "id" attribute is defined for this element, then it's set to a likely- to-be-unique value, and returned. (The "f" is for "force".) STRUCTURE-MODIFYING METHODS These methods are provided for modifying the content of trees by adding or changing nodes as parents or children of other nodes. push_content $h->push_content($element_or_text, ...); Adds the specified items to the end of the content list of the element $h. The items of content to be added should each be either a text segment (a string), an HTML::Element object, or an arrayref. Arrayrefs are fed thru "$h->new_from_lol(that_arrayref)" to convert them into elements, before being added to the content list of $h. This means you can say things concise things like: $body->push_content( ['br'], ['ul', map ['li', $_], qw(Peaches Apples Pears Mangos) ] ); See the "new_from_lol" method's documentation, far below, for more explanation. Returns $h (the element itself). The push_content method will try to consolidate adjacent text segments while adding to the content list. That's to say, if $h's "content_list" is ('foo bar ', $some_node, 'baz!') and you call $h->push_content('quack?'); then the resulting content list will be this: ('foo bar ', $some_node, 'baz!quack?') and not this: ('foo bar ', $some_node, 'baz!', 'quack?') If that latter is what you want, you'll have to override the feature of consolidating text by using splice_content, as in: $h->splice_content(scalar($h->content_list),0,'quack?'); Similarly, if you wanted to add 'Skronk' to the beginning of the content list, calling this: $h->unshift_content('Skronk'); then the resulting content list will be this: ('Skronkfoo bar ', $some_node, 'baz!') and not this: ('Skronk', 'foo bar ', $some_node, 'baz!') What you'd to do get the latter is: $h->splice_content(0,0,'Skronk'); unshift_content $h->unshift_content($element_or_text, ...) Just like "push_content", but adds to the beginning of the $h element's content list. The items of content to be added should each be either a text segment (a string), an HTML::Element object, or an arrayref (which is fed thru "new_from_lol"). The unshift_content method will try to consolidate adjacent text segments while adding to the content list. See above for a discussion of this. Returns $h (the element itself). splice_content @removed = $h->splice_content($offset, $length, $element_or_text, ...); Detaches the elements from $h's list of content-nodes, starting at $offset and continuing for $length items, replacing them with the elements of the following list, if any. Returns the elements (if any) removed from the content-list. If $offset is negative, then it starts that far from the end of the array, just like Perl's normal "splice" function. If $length and the following list is omitted, removes everything from $offset onward. The items of content to be added (if any) should each be either a text segment (a string), an arrayref (which is fed thru "new_from_lol"), or an HTML::Element object that's not already a child of $h. detach $old_parent = $h->detach(); This unlinks $h from its parent, by setting its 'parent' attribute to undef, and by removing it from the content list of its parent (if it had one). The return value is the parent that was detached from (or undef, if $h had no parent to start with). Note that neither $h nor its parent are explicitly destroyed. detach_content @old_content = $h->detach_content(); This unlinks all of $h's children from $h, and returns them. Note that these are not explicitly destroyed; for that, you can just use "$h->delete_content". replace_with $h->replace_with( $element_or_text, ... ) This replaces $h in its parent's content list with the nodes specified. The element $h (which by then may have no parent) is returned. This causes a fatal error if $h has no parent. The list of nodes to insert may contain $h, but at most once. Aside from that possible exception, the nodes to insert should not already be children of $h's parent. Also, note that this method does not destroy $h if weak references are turned off -- use "$h->replace_with(...)->delete" if you need that. preinsert $h->preinsert($element_or_text...); Inserts the given nodes right BEFORE $h in $h's parent's content list. This causes a fatal error if $h has no parent. None of the given nodes should be $h or other children of $h. Returns $h. postinsert $h->postinsert($element_or_text...) Inserts the given nodes right AFTER $h in $h's parent's content list. This causes a fatal error if $h has no parent. None of the given nodes should be $h or other children of $h. Returns $h. replace_with_content $h->replace_with_content(); This replaces $h in its parent's content list with its own content. The element $h (which by then has no parent or content of its own) is returned. This causes a fatal error if $h has no parent. Also, note that this does not destroy $h if weak references are turned off -- use "$h->replace_with_content->delete" if you need that. delete_content $h->delete_content(); $h->destroy_content(); # alias Clears the content of $h, calling "$h->delete" for each content element. Compare with "$h->detach_content". Returns $h. "destroy_content" is an alias for this method. delete $h->delete(); $h->destroy(); # alias Detaches this element from its parent (if it has one) and explicitly destroys the element and all its descendants. The return value is the empty list (or "undef" in scalar context). Before version 5.00 of HTML::Element, you had to call "delete" when you were finished with the tree, or your program would leak memory. This is no longer necessary if weak references are enabled, see "Weak References". destroy An alias for "delete". destroy_content An alias for "delete_content". clone $copy = $h->clone(); Returns a copy of the element (whose children are clones (recursively) of the original's children, if any). The returned element is parentless. Any '_pos' attributes present in the source element/tree will be absent in the copy. For that and other reasons, the clone of an HTML::TreeBuilder object that's in mid-parse (i.e, the head of a tree that HTML::TreeBuilder is elaborating) cannot (currently) be used to continue the parse. You are free to clone HTML::TreeBuilder trees, just as long as: 1) they're done being parsed, or 2) you don't expect to resume parsing into the clone. (You can continue parsing into the original; it is never affected.) clone_list @copies = HTML::Element->clone_list(...nodes...); Returns a list consisting of a copy of each node given. Text segments are simply copied; elements are cloned by calling "$it->clone" on each of them. Note that this must be called as a class method, not as an instance method. "clone_list" will croak if called as an instance method. You can also call it like so: ref($h)->clone_list(...nodes...) normalize_content $h->normalize_content Normalizes the content of $h -- i.e., concatenates any adjacent text nodes. (Any undefined text segments are turned into empty-strings.) Note that this does not recurse into $h's descendants. delete_ignorable_whitespace $h->delete_ignorable_whitespace() This traverses under $h and deletes any text segments that are ignorable whitespace. You should not use this if $h is under a "
"
       element.

   insert_element
         $h->insert_element($element, $implicit);

       Inserts (via push_content) a new element under the element at
       "$h->pos()".  Then updates "$h->pos()" to point to the inserted
       element, unless $element is a prototypically empty element like "
",
       "
", "", etc.  The new "$h->pos()" is returned.  This method is
       useful only if your particular tree task involves setting "$h->pos()".

DUMPING METHODS
   dump
         $h->dump()
         $h->dump(*FH)  ; # or *FH{IO} or $fh_obj

       Prints the element and all its children to STDOUT (or to a specified
       filehandle), in a format useful only for debugging.  The structure of
       the document is shown by indentation (no end tags).

   as_HTML
         $s = $h->as_HTML();
         $s = $h->as_HTML($entities);
         $s = $h->as_HTML($entities, $indent_char);
         $s = $h->as_HTML($entities, $indent_char, \%optional_end_tags);

       Returns a string representing in HTML the element and its descendants.
       The optional argument $entities specifies a string of the entities to
       encode.  For compatibility with previous versions, specify '<>&' here.
       If omitted or undef, all unsafe characters are encoded as HTML
       entities.  See HTML::Entities for details.  If passed an empty string,
       no entities are encoded.

       If $indent_char is specified and defined, the HTML to be output is
       intented, using the string you specify (which you probably should set
       to "\t", or some number of spaces, if you specify it).

       If "\%optional_end_tags" is specified and defined, it should be a
       reference to a hash that holds a true value for every tag name whose
       end tag is optional.  Defaults to "\%HTML::Element::optionalEndTag",
       which is an alias to %HTML::Tagset::optionalEndTag, which, at time of
       writing, contains true values for "p, li, dt, dd".  A useful value to
       pass is an empty hashref, "{}", which means that no end-tags are
       optional for this dump.  Otherwise, possibly consider copying
       %HTML::Tagset::optionalEndTag to a hash of your own, adding or deleting
       values as you like, and passing a reference to that hash.

   as_text
         $s = $h->as_text();
         $s = $h->as_text(skip_dels => 1);

       Returns a string consisting of only the text parts of the element's
       descendants.  Any whitespace inside the element is included unchanged,
       but whitespace not in the tree is never added.  But remember that
       whitespace may be ignored or compacted by HTML::TreeBuilder during
       parsing (depending on the value of the "ignore_ignorable_whitespace"
       and "no_space_compacting" attributes).  Also, since whitespace is never
       added during parsing,

         HTML::TreeBuilder->new_from_content("
a
b
")
                          ->as_text;

       returns "ab", not "a b" or "a\nb".

       Text under "