Module: Nokogiri::HTML5

Defined in:



HTML5 functionality is not available when running JRuby.


Parse an HTML5 document:

doc = Nokogiri.HTML5(string)

Parse an HTML5 fragment:

fragment = Nokogiri::HTML5.fragment(string)

Parsing options

The document and fragment parsing methods support options that are different from Nokogiri's.

  • Nokogiri.HTML5(html, url = nil, encoding = nil, options = {})

  • Nokogiri::HTML5.parse(html, url = nil, encoding = nil, options = {})

  • Nokogiri::HTML5::Document.parse(html, url = nil, encoding = nil, options = {})

  • Nokogiri::HTML5.fragment(html, encoding = nil, options = {})

  • Nokogiri::HTML5::DocumentFragment.parse(html, encoding = nil, options = {})

The three currently supported options are :max_errors, :max_tree_depth and :max_attributes, described below.

Error reporting

Nokogiri contains an experimental HTML5 parse error reporting facility. By default, no parse errors are reported but this can be configured by passing the :max_errors option to HTML5.parse or HTML5.fragment.

For example, this script:

doc = Nokogiri::HTML5.parse('<span/>Hi there!</span foo=bar />', max_errors: 10)
doc.errors.each do |err|


1:1: ERROR: Expected a doctype token
<span/>Hi there!</span foo=bar />
1:1: ERROR: Start tag of nonvoid HTML element ends with '/>', use '>'.
<span/>Hi there!</span foo=bar />
1:17: ERROR: End tag ends with '/>', use '>'.
<span/>Hi there!</span foo=bar />
1:17: ERROR: End tag contains attributes.
<span/>Hi there!</span foo=bar />

Using max_errors: -1 results in an unlimited number of errors being returned.

The errors returned by XML::Document#errors are instances of XML::SyntaxError.

The HTML standard defines a number of standard parse error codes. These error codes only cover the “tokenization” stage of parsing HTML. The parse errors in the “tree construction” stage do not have standardized error codes (yet).

As a convenience to Nokogiri users, the defined error codes are available via XML::SyntaxError#str1 method.

doc = Nokogiri::HTML5.parse('<span/>Hi there!</span foo=bar />', max_errors: 10)
doc.errors.each do |err|
  puts("#{err.line}:#{err.column}: #{err.str1}")
# => 1:1: generic-parser
#    1:1: non-void-html-element-start-tag-with-trailing-solidus
#    1:17: end-tag-with-trailing-solidus
#    1:17: end-tag-with-attributes

Note that the first error is generic-parser because it's an error from the tree construction stage and doesn't have a standardized error code.

For the purposes of semantic versioning, the error messages, error locations, and error codes are not part of Nokogiri's public API. That is, these are subject to change without Nokogiri's major version number changing. These may be stabilized in the future.

Maximum tree depth

The maximum depth of the DOM tree parsed by the various parsing methods is configurable by the :max_tree_depth option. If the depth of the tree would exceed this limit, then an ArgumentError is thrown.

This limit (which defaults to Nokogiri::Gumbo::DEFAULT_MAX_TREE_DEPTH = 400) can be removed by giving the option max_tree_depth: -1.

html = '<!DOCTYPE html>' + '<div>' * 1000
doc = Nokogiri.HTML5(html)
# raises ArgumentError: Document tree depth limit exceeded
doc = Nokogiri.HTML5(html, max_tree_depth: -1)

Attribute limit per element

The maximum number of attributes per DOM element is configurable by the :max_attributes option. If a given element would exceed this limit, then an ArgumentError is thrown.

This limit (which defaults to Nokogiri::Gumbo::DEFAULT_MAX_ATTRIBUTES = 400) can be removed by giving the option max_attributes: -1.

html = '<!DOCTYPE html><div ' + (1..1000).map { |x| "attr-#{x}" }.join(' ') + '>'
# "<!DOCTYPE html><div attr-1 attr-2 attr-3 ... attr-1000>"
doc = Nokogiri.HTML5(html)
# raises ArgumentError: Attributes per element limit exceeded
doc = Nokogiri.HTML5(html, max_attributes: -1)

HTML Serialization

After parsing HTML, it may be serialized using any of the XML::Node serialization methods. In particular, XML::Node#serialize, XML::Node#to_html, and XML::Node#to_s will serialize a given node and its children. (This is the equivalent of JavaScript's Element.outerHTML.) Similarly, XML::Node#inner_html will serialize the children of a given node. (This is the equivalent of JavaScript's Element.innerHTML.)

doc = Nokogiri::HTML5("<!DOCTYPE html><span>Hello world!</span>")
puts doc.serialize
# => <!DOCTYPE html><html><head></head><body><span>Hello world!</span></body></html>

Due to quirks in how HTML is parsed and serialized, it's possible for a DOM tree to be serialized and then re-parsed, resulting in a different DOM. Mostly, this happens with DOMs produced from invalid HTML. Unfortunately, even valid HTML may not survive serialization and re-parsing.

In particular, a newline at the start of pre, listing, and textarea elements is ignored by the parser.

doc = Nokogiri::HTML5(<<-EOF)
<!DOCTYPE html>
# => <pre>Content</pre>

In this case, the original HTML is semantically equivalent to the serialized version. If the pre, listing, or textarea content starts with two newlines, the first newline will be stripped on the first parse and the second newline will be stripped on the second, leading to semantically different DOMs. Passing the parameter preserve_newline: true will cause two or more newlines to be preserved. (A single leading newline will still be removed.)

doc = Nokogiri::HTML5(<<-EOF)
<!DOCTYPE html>

puts'/html/body/listing').serialize(preserve_newline: true)
# => <listing>
#    Content</listing>


Nokogiri always parses HTML5 using UTF-8; however, the encoding of the input can be explicitly selected via the optional encoding parameter. This is most useful when the input comes not from a string but from an IO object.

When serializing a document or node, the encoding of the output string can be specified via the :encoding options. Characters that cannot be encoded in the selected encoding will be encoded as HTML numeric entities.

frag = Nokogiri::HTML5.fragment('<span>아는 길도 물어가라</span>')
html = frag.serialize(encoding: 'US-ASCII')
puts html
# => <span>&#xc544;&#xb294; &#xae38;&#xb3c4; &#xbb3c;&#xc5b4;&#xac00;&#xb77c;</span>
frag = Nokogiri::HTML5.fragment(html)
puts frag.serialize
# => <span>아는 길도 물어가라</span>

(There's a bug in all current versions of Ruby that can cause the entity encoding to fail. Of the mandated supported encodings for HTML, the only encoding I'm aware of that has this bug is 'ISO-2022-JP'. We recommend avoiding this encoding.)


  • The HTML5.fragment function takes a string and parses it as a HTML5 document. The <html>, <head>, and <body> elements are removed from this document, and any children of these elements that remain are returned as a DocumentFragment.

  • The HTML5.parse function takes a string and passes it to the gumbo_parse_with_options method, using the default options. The resulting Gumbo parse tree is then walked.

  • Instead of uppercase element names, lowercase element names are produced.

  • Instead of returning unknown as the element name for unknown tags, the original tag name is returned verbatim.


  • v1.12.0

Defined Under Namespace

Modules: Node Classes: Document, DocumentFragment

Constant Summary collapse


HTML uses the XHTML namespace.


  • v1.12.0



  • v1.12.0



  • v1.12.0



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  • v1.12.0


Class Method Summary collapse

Methods included from Node

#fragment, #inner_html, #write_to

Class Method Details

.fragment(string, encoding = nil, **options) ⇒ Object

Parse a fragment from string. Convenience method for Nokogiri::HTML5::DocumentFragment.parse.


  • v1.12.0

# File 'lib/nokogiri/html5.rb', line 241

def self.fragment(string, encoding = nil, **options)
  DocumentFragment.parse(string, encoding, options)

.get(uri, options = {}) ⇒ Object

Fetch and parse a HTML document from the web, following redirects, handling https, and determining the character encoding using HTML5 rules. uri may be a String or a URI. options contains http headers and special options. Everything which is not a special option is considered a header. Special options include:

* :follow_limit => number of redirects which are followed
* :basic_auth => [username, password]


  • v1.12.0

# File 'lib/nokogiri/html5.rb', line 252

def self.get(uri, options={})
  warn("Nokogiri::HTML5.get is deprecated and will be removed in a future version of Nokogiri.",
       uplevel: 1, category: :deprecated)
  get_impl(uri, options)

.parse(string, url = nil, encoding = nil, **options, &block) ⇒ Object

Parse an HTML 5 document. Convenience method for Nokogiri::HTML5::Document.parse


  • v1.12.0

# File 'lib/nokogiri/html5.rb', line 235

def self.parse(string, url = nil, encoding = nil, **options, &block)
  Document.parse(string, url, encoding, **options, &block)