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Provides methods to generate HTML tags programmatically both as a modern HTML5 compliant builder style and legacy XHTML compliant tags.

Included Modules
ARIA_PREFIXES = ["aria", :aria].to_set.freeze
BOOLEAN_ATTRIBUTES = %w(allowfullscreen allowpaymentrequest async autofocus autoplay checked compact controls declare default defaultchecked defaultmuted defaultselected defer disabled enabled formnovalidate hidden indeterminate inert ismap itemscope loop multiple muted nohref nomodule noresize noshade novalidate nowrap open pauseonexit playsinline readonly required reversed scoped seamless selected sortable truespeed typemustmatch visible).to_set
DATA_PREFIXES = ["data", :data].to_set.freeze
PRE_CONTENT_STRINGS = Hash.new { "" }
Class Public methods
# File actionview/lib/action_view/helpers/tag_helper.rb, line 364
def build_tag_values(*args)
  tag_values = []

  args.each do |tag_value|
    case tag_value
    when Hash
      tag_value.each do |key, val|
        tag_values << key.to_s if val && key.present?
    when Array
      tag_values.concat build_tag_values(*tag_value)
      tag_values << tag_value.to_s if tag_value.present?

Instance Public methods

Returns a CDATA section with the given content. CDATA sections are used to escape blocks of text containing characters which would otherwise be recognized as markup. CDATA sections begin with the string <![CDATA[ and end with (and may not contain) the string ]]>.

cdata_section("<hello world>")
# => <![CDATA[<hello world>]]>

# => <![CDATA[<hello from a text file]]>

# => <![CDATA[hello]]]]><![CDATA[>world]]>
# File actionview/lib/action_view/helpers/tag_helper.rb, line 347
def cdata_section(content)
  splitted = content.to_s.gsub(/\]\]\>/, "]]]]><![CDATA[>")
Alias for: token_list
content_tag(name, content_or_options_with_block = nil, options = nil, escape = true, &block)

Returns an HTML block tag of type name surrounding the content. Add HTML attributes by passing an attributes hash to options. Instead of passing the content as an argument, you can also use a block in which case, you pass your options as the second parameter. Set escape to false to disable attribute value escaping. Note: this is legacy syntax, see tag method description for details.


The options hash can be used with attributes with no value like (disabled and readonly), which you can give a value of true in the options hash. You can use symbols or strings for the attribute names.


content_tag(:p, "Hello world!")
 # => <p>Hello world!</p>
content_tag(:div, content_tag(:p, "Hello world!"), class: "strong")
 # => <div class="strong"><p>Hello world!</p></div>
content_tag(:div, "Hello world!", class: ["strong", "highlight"])
 # => <div class="strong highlight">Hello world!</div>
content_tag(:div, "Hello world!", class: ["strong", { highlight: current_user.admin? }])
 # => <div class="strong highlight">Hello world!</div>
content_tag("select", options, multiple: true)
 # => <select multiple="multiple">...options...</select>

<%= content_tag :div, class: "strong" do -%>
  Hello world!
<% end -%>
 # => <div class="strong">Hello world!</div>
# File actionview/lib/action_view/helpers/tag_helper.rb, line 307
def content_tag(name, content_or_options_with_block = nil, options = nil, escape = true, &block)
  if block_given?
    options = content_or_options_with_block if content_or_options_with_block.is_a?(Hash)
    tag_builder.content_tag_string(name, capture(&block), options, escape)
    tag_builder.content_tag_string(name, content_or_options_with_block, options, escape)

Returns an escaped version of html without affecting existing escaped entities.

escape_once("1 < 2 &amp; 3")
# => "1 &lt; 2 &amp; 3"

escape_once("&lt;&lt; Accept & Checkout")
# => "&lt;&lt; Accept &amp; Checkout"
# File actionview/lib/action_view/helpers/tag_helper.rb, line 359
def escape_once(html)
tag(name = nil, options = nil, open = false, escape = true)

Returns an HTML tag.

Building HTML tags

Builds HTML5 compliant tags with a tag proxy. Every tag can be built with:

tag.<tag name>(optional content, options)

where tag name can be e.g. br, div, section, article, or any tag really.

Passing content

Tags can pass content to embed within it:

tag.h1 'All titles fit to print' # => <h1>All titles fit to print</h1>

tag.div tag.p('Hello world!')  # => <div><p>Hello world!</p></div>

Content can also be captured with a block, which is useful in templates:

<%= tag.p do %>
  The next great American novel starts here.
<% end %>
# => <p>The next great American novel starts here.</p>


Use symbol keyed options to add attributes to the generated tag.

tag.section class: %w( kitties puppies )
# => <section class="kitties puppies"></section>

tag.section id: dom_id(@post)
# => <section id="<generated dom id>"></section>

Pass true for any attributes that can render with no values, like disabled and readonly.

tag.input type: 'text', disabled: true
# => <input type="text" disabled="disabled">

HTML5 data-* and aria-* attributes can be set with a single data or aria key pointing to a hash of sub-attributes.

To play nicely with JavaScript conventions, sub-attributes are dasherized.

tag.article data: { user_id: 123 }
# => <article data-user-id="123"></article>

Thus data-user-id can be accessed as dataset.userId.

Data attribute values are encoded to JSON, with the exception of strings, symbols and BigDecimals. This may come in handy when using jQuery's HTML5-aware .data() from 1.4.3.

tag.div data: { city_state: %w( Chicago IL ) }
# => <div data-city-state="[&quot;Chicago&quot;,&quot;IL&quot;]"></div>

The generated attributes are escaped by default. This can be disabled using escape_attributes.

tag.img src: 'open & shut.png'
# => <img src="open &amp; shut.png">

tag.img src: 'open & shut.png', escape_attributes: false
# => <img src="open & shut.png">

The tag builder respects HTML5 void elements if no content is passed, and omits closing tags for those elements.

# A standard element:
tag.div # => <div></div>

# A void element:
tag.br  # => <br>

Legacy syntax

The following format is for legacy syntax support. It will be deprecated in future versions of Rails.

tag(name, options = nil, open = false, escape = true)

It returns an empty HTML tag of type name which by default is XHTML compliant. Set open to true to create an open tag compatible with HTML 4.0 and below. Add HTML attributes by passing an attributes hash to options. Set escape to false to disable attribute value escaping.


You can use symbols or strings for the attribute names.

Use true with boolean attributes that can render with no value, like disabled and readonly.

HTML5 data-* attributes can be set with a single data key pointing to a hash of sub-attributes.


# => <br />

tag("br", nil, true)
# => <br>

tag("input", type: 'text', disabled: true)
# => <input type="text" disabled="disabled" />

tag("input", type: 'text', class: ["strong", "highlight"])
# => <input class="strong highlight" type="text" />

tag("img", src: "open & shut.png")
# => <img src="open &amp; shut.png" />

tag("img", { src: "open &amp; shut.png" }, false, false)
# => <img src="open &amp; shut.png" />

tag("div", data: { name: 'Stephen', city_state: %w(Chicago IL) })
# => <div data-name="Stephen" data-city-state="[&quot;Chicago&quot;,&quot;IL&quot;]" />

tag("div", class: { highlight: current_user.admin? })
# => <div class="highlight" />
# File actionview/lib/action_view/helpers/tag_helper.rb, line 271
def tag(name = nil, options = nil, open = false, escape = true)
  if name.nil?
    "<#{name}#{tag_builder.tag_options(options, escape) if options}#{open ? ">" : " />"}".html_safe

Returns a string of tokens built from args.


token_list("foo", "bar")
 # => "foo bar"
token_list("foo", "foo bar")
 # => "foo bar"
token_list({ foo: true, bar: false })
 # => "foo"
token_list(nil, false, 123, "", "foo", { bar: true })
 # => "123 foo bar"
Also aliased as: class_names
# File actionview/lib/action_view/helpers/tag_helper.rb, line 327
def token_list(*args)
  tokens = build_tag_values(*args).flat_map { |value| value.to_s.split(/\s+/) }.uniq

  safe_join(tokens, " ")