### Nokogiri Setup Code

Source: https://github.com/sparklemotion/nokogiri/blob/main/doc/keyword_arguments.md

Provides the necessary setup code, including require statements and variable initializations, for running Nokogiri examples.

```ruby
require 'nokogiri'
include Nokogiri
xml_s = '<root />'
url = 'www.site.com'
encoding = 'UTF-16'
options = XML::ParseOptions::STRICT
```

--------------------------------

### Successful Native Gem Installation Example

Source: https://github.com/sparklemotion/nokogiri/blob/main/README.md

This output shows a successful installation of a native Nokogiri gem, indicating pre-compiled libraries were used. This typically results in faster and more reliable installations.

```sh
$ gem install nokogiri
Fetching nokogiri-1.11.0-x86_64-linux.gem
Successfully installed nokogiri-1.11.0-x86_64-linux
1 gem installed

```

--------------------------------

### Install libiconv using Homebrew

Source: https://github.com/sparklemotion/nokogiri/wiki/Install-libiconv-on-OS-X-with-Homebrew

Use this command to install the libiconv package via Homebrew.

```bash
brew install libiconv
```

--------------------------------

### Install Nokogiri with Custom Library Paths

Source: https://github.com/sparklemotion/nokogiri/wiki/Install-libiconv-on-OS-X-with-Homebrew

Install Nokogiri specifying custom include and library paths for libxml2, libxslt, and libiconv. This is useful when system versions are outdated or non-standard.

```bash
gem install nokogiri -- --with-xml2-include=/usr/local/Cellar/libxml2/2.7.8/include/libxml2 --with-xml2-lib=/usr/local/Cellar/libxml2/2.7.8/lib --with-xslt-dir=/usr/local/Cellar/libxslt/1.1.26 --with-iconv-include=/usr/local/Cellar/libiconv/1.15/include --with-iconv-lib=/usr/local/Cellar/libiconv/1.15/lib
```

--------------------------------

### Clone Nokogiri Repository and Install Dependencies

Source: https://github.com/sparklemotion/nokogiri/blob/main/CONTRIBUTING.md

This snippet shows the basic steps to clone the Nokogiri repository and install its dependencies using Bundler.

```sh
git clone --recurse-submodules https://github.com/sparklemotion/nokogiri
cd nokogiri
bundle install
```

--------------------------------

### Install Nokogiri with Homebrew's libiconv

Source: https://github.com/sparklemotion/nokogiri/wiki/Install-libiconv-on-OS-X-with-Homebrew

Install the Nokogiri gem, specifying the path to the libiconv installed by Homebrew. This is necessary if Nokogiri reports an outdated libiconv version.

```bash
gem install nokogiri -- --with-iconv-dir=/usr/local/Cellar/libiconv/1.15/
```

--------------------------------

### RDoc Documentation Example

Source: https://github.com/sparklemotion/nokogiri/blob/main/CONTRIBUTING.md

Illustrates the use of `:call-seq:`, parameter types, return types, and callouts for documentation strings.

```ruby
module Nokogiri
  module XML
    class Node
      # :call-seq: upcase(name) → String
      # Returns the uppercase version of the given name.
      #
      # [Parameters]
      #   * name (String): the name to uppercase
      #
      # [Returns]
      #   String: the uppercased name
      #
      # 💡 This method is a simple wrapper around String#upcase.
      def upcase(name)
        name.upcase
      end
    end
  end
end
```

--------------------------------

### C Function Naming Convention Example

Source: https://github.com/sparklemotion/nokogiri/blob/main/CONTRIBUTING.md

Demonstrates the naming conventions for public and static functions in C code.

```c
/* Public function, bound to Ruby method */
int noko_xml_sax_parser_context_...(...);

/* Static function (file scope) */
int xml_sax_parser_context_...(...);
```

--------------------------------

### Dockerfile for Nokogiri Installation

Source: https://github.com/sparklemotion/nokogiri/wiki/Running-in-a-docker-(Ubuntu)

This Dockerfile installs necessary system packages, Ruby, and configures Nokogiri for installation within an Ubuntu environment. It specifies environment variables and dependencies required for Nokogiri.

```docker
FROM  ubuntu:latest

RUN apt-get update
RUN apt-get install -y make curl

# ruby's nokorigi is sometimes described as being 'hard' to install, but the below 2 instructions, bundled with the version specified in Gemfile* make it install nicely
RUN echo 'LC_ALL="en_US.UTF-8"' > /etc/default/locale
RUN apt-get install -y ruby1.9.3

# greatly speeds up nokogiri install
ENV NOKOGIRI_USE_SYSTEM_LIBRARIES 1
# dependencies for nokogiri gem
RUN apt-get install -y libxml2 libxml2-dev libxslt1-dev

# install bundler
RUN gem install bundler

# install gems
ADD Gemfile /tmp/
ADD Gemfile.lock /tmp/
RUN cd /tmp; bundle install
```

--------------------------------

### Rails Controller Example

Source: https://github.com/sparklemotion/nokogiri/blob/main/test/files/tlm.html

A basic Rails controller that fetches a list of users. This data will be accessible in the JavaScript view.

```ruby
class JohnsonController < ApplicationController
  def index
    @users = User.find(:all)
  end
end
```

--------------------------------

### C Ruby Instance Method Naming Example

Source: https://github.com/sparklemotion/nokogiri/blob/main/CONTRIBUTING.md

Illustrates the naming convention for C functions corresponding to Ruby instance methods.

```c
/* Ruby instance method: Nokogiri::XML::SAX::ParserContext#line */
int noko_xml_sax_parser_context__line(...);
```

--------------------------------

### C Ruby Singleton Method Naming Example

Source: https://github.com/sparklemotion/nokogiri/blob/main/CONTRIBUTING.md

Shows the naming convention for C functions corresponding to Ruby singleton methods.

```c
/* Ruby singleton method: Nokogiri::XML::SAX::ParserContext.io */
int noko_xml_sax_parser_context_s_io(...);
```

--------------------------------

### Run Focused Tests with Minitest Options

Source: https://github.com/sparklemotion/nokogiri/blob/main/CONTRIBUTING.md

Use TESTOPTS to run specific tests, for example, tests matching a particular pattern.

```sh
bundle exec rake compile test TESTOPTS="-n/test_last_element_child/"
```

--------------------------------

### Successful Fuzzer Output Example

Source: https://github.com/sparklemotion/nokogiri/blob/main/CONTRIBUTING.md

This output indicates the fuzzer is running successfully, collecting coverage, and finding new code paths. It is typical during normal fuzzing operations.

```text
INFO: Seed: 4156947595
INFO: Loaded 1 modules   (7149 inline 8-bit counters): 7149 0x58a462, 0x58c04f, 
INFO: Loaded 1 PC tables (7149 PCs): 7149 0x53beb0,0x557d80, 
INFO: -max_len is not provided; libFuzzer will not generate inputs larger than 4096 bytes
INFO: A corpus is not provided, starting from an empty corpus
#2	INITED cov: 2 ft: 2 corp: 1/1b exec/s: 0 rss: 24Mb
	NEW_FUNC[1/44]: 0x429840 in gumbo_parse_with_options (/home/user/nokogiri/gumbo-parser/fuzzer/build/parse_fuzzer+0x429840)
	NEW_FUNC[2/44]: 0x42c0d0 in destroy_node (/home/user/nokogiri/gumbo-parser/fuzzer/build/parse_fuzzer+0x42c0d0)
#721	NEW    cov: 180 ft: 181 corp: 2/12b lim: 11 exec/s: 0 rss: 27Mb L: 11/11 MS: 4 ChangeByte-ChangeByte-ChangeBit-InsertRepeatedBytes-
#722	NEW    cov: 186 ft: 196 corp: 3/23b lim: 11 exec/s: 0 rss: 27Mb L: 11/11 MS: 1 ChangeBit-
#723	NEW    cov: 186 ft: 228 corp: 4/34b lim: 11 exec/s: 0 rss: 27Mb L: 11/11 MS: 1 ChangeBinInt-
#724	NEW    cov: 188 ft: 241 corp: 5/45b lim: 11 exec/s: 0 rss: 27Mb L: 11/11 MS: 1 ChangeBit-
#725	NEW    cov: 188 ft: 254 corp: 6/56b lim: 11 exec/s: 0 rss: 27Mb L: 11/11 MS: 1 ChangeByte-
#726	NEW    cov: 188 ft: 270 corp: 7/67b lim: 11 exec/s: 0 rss: 27Mb L: 11/11 MS: 1 CopyPart-
#732	NEW    cov: 188 ft: 279 corp: 8/78b lim: 11 exec/s: 0 rss: 27Mb L: 11/11 MS: 1 ChangeBit-
	NEW_FUNC[1/1]: 0x441de0 in gumbo_token_destroy (/home/user/nokogiri/gumbo-parser/fuzzer/build/parse_fuzzer+0x441de0)

```

--------------------------------

### Ruby Object#tase! Method Example

Source: https://github.com/sparklemotion/nokogiri/blob/main/test/files/tlm.html

Demonstrates the custom Object#tase! method available in the Brobinius Ruby implementation, which raises a RuntimeError.

```ruby
>> x = Class.new
=> #<Class:0x3632ec>
>> x.tase!
RuntimeError: Don't tase me bro
from (irb):2:in `tase!'
from (irb):6
>>
```

--------------------------------

### Slop Decorator HTML Example

Source: https://github.com/sparklemotion/nokogiri/wiki/Cheat-sheet

Demonstrates accessing HTML elements and their text content using the Slop decorator's method-based syntax.

```ruby
doc = Nokogiri::Slop(<<-eohtml)
  <html>
    <body>
      <p>first</p>
      <p>second</p>
    </body>
  </html>
eohtml
assert_equal('second', doc.html.body.p[1].text)
```

--------------------------------

### Rewrite Ruby Object Access Example Entirely in JavaScript

Source: https://github.com/sparklemotion/nokogiri/blob/main/test/files/tlm.html

Shows how to create a Ruby Struct and assign a property to it entirely within JavaScript, using the 'Ruby' variable for access.

```ruby
ctx = Johnson::Context.new
ctx.evaluate("var x = new (new Ruby.Struct(Johnson.symbolize('foo')));")
ctx.evaluate("x.foo = 'bar'")
puts ctx.evaluate('x').foo
puts ctx.evaluate('x').class
```

--------------------------------

### Get Namespace Definitions

Source: https://github.com/sparklemotion/nokogiri/wiki/Cheat-sheet

Returns an array of Namespace objects defined directly on this node, including default and prefixed namespaces.

```ruby
node.namespace_definitions
```

--------------------------------

### C Ruby Attribute Getter/Setter Naming Example

Source: https://github.com/sparklemotion/nokogiri/blob/main/CONTRIBUTING.md

Demonstrates the naming conventions for C functions representing Ruby attribute getters and setters.

```c
/* Ruby attribute setter: Nokogiri::XML::SAX::ParserContext#recovery= */
int noko_xml_sax_parser_context__recovery_set(...);

/* Ruby attribute getter: Nokogiri::XML::SAX::ParserContext#recovery */
int noko_xml_sax_parser_context__recovery_get(...);
```

--------------------------------

### CSS Parsing with Nokogiri

Source: https://github.com/sparklemotion/nokogiri/wiki/Cheat-sheet

Provides examples for parsing CSS selectors using Nokogiri. It shows how to parse a selector into an Abstract Syntax Tree (AST) and convert it to an XPath expression.

```ruby
# https://nokogiri.org/rdoc/Nokogiri/CSS.html
Nokogiri::CSS.parse('selector') # => returns an AST
Nokogiri::CSS.xpath_for('selector', options={})
 
# https://nokogiri.org/rdoc/Nokogiri/CSS/Node.html
  # attr: type, value
  #methods
  # accept(visitor)
  # find_by_type
  # new
  # preprocess!
  # to_a
  # to_type
  # to_xpath
# https://nokogiri.org/rdoc/Nokogiri/CSS/Parser.html # a Racc generated Parser
```

--------------------------------

### Compile and Test with System Libraries

Source: https://github.com/sparklemotion/nokogiri/blob/main/CONTRIBUTING.md

Clean previous builds and then compile and run tests, explicitly enabling the use of system libraries.

```sh
bundle exec rake clean  #  blow away pre-existing libraries using packaged libs
bundle exec rake compile test -- --enable-system-libraries
```

--------------------------------

### Run Performance Benchmarks

Source: https://github.com/sparklemotion/nokogiri/blob/main/CONTRIBUTING.md

Compile the extension and run the performance benchmark tests.

```sh
bundle exec rake compile test:bench
```

--------------------------------

### Initialize Submodule and Run Tests

Source: https://github.com/sparklemotion/nokogiri/blob/main/CONTRIBUTING.md

Initialize the html5lib-tests submodule and then run the Nokogiri compile and test tasks. This is necessary if the submodule has not been checked out.

```sh
git submodule update --init  #  test/html5lib-tests
bundle exec rake compile test
```

--------------------------------

### EJS JavaScript View Example

Source: https://github.com/sparklemotion/nokogiri/blob/main/test/files/tlm.html

An example of an EJS (Embedded JavaScript) view that iterates over users passed from the controller. It uses the 'at' object to access controller instance variables.

```javascript
<% for(var user in at.users) {
  %><%= user.first_name() %><br />
<% }
%>
```

--------------------------------

### Log in to a website

Source: https://github.com/sparklemotion/nokogiri/blob/main/test/files/tlm.html

Instantiate a Mechanize agent, fetch a URL, set login credentials, and submit the login form. Ensure the user agent alias is set appropriately.

```ruby
agent = WWW::Mechanize.new { |a|  
  a.user_agent_alias = 'Mac Safari'  
}
page = agent.get('http://youtube.com/')

# Login  
page.form('loginForm') { |f|  
  f.username = 'username'
  f.password = 'password'
}.submit
```

--------------------------------

### Get Internal Subset

Source: https://github.com/sparklemotion/nokogiri/wiki/Cheat-sheet

Retrieve the internal subset of the DTD.

```ruby
node.internal_subset
```

--------------------------------

### Get External Subset

Source: https://github.com/sparklemotion/nokogiri/wiki/Cheat-sheet

Retrieve the external subset of the DTD.

```ruby
node.external_subset
```

--------------------------------

### Run Tests with Valgrind

Source: https://github.com/sparklemotion/nokogiri/blob/main/CONTRIBUTING.md

Compile the extension and run the test suite under Valgrind for memory error detection.

```sh
bundle exec rake compile test:valgrind
```

--------------------------------

### Get Node Path

Source: https://github.com/sparklemotion/nokogiri/wiki/Cheat-sheet

Returns the XPath-like path associated with this node.

```ruby
node.path
```

--------------------------------

### Get Node CSS Path

Source: https://github.com/sparklemotion/nokogiri/wiki/Cheat-sheet

Returns the path to this node expressed as a CSS selector.

```ruby
node.css_path
```

--------------------------------

### Get Ancestor Nodes

Source: https://github.com/sparklemotion/nokogiri/wiki/Cheat-sheet

Returns a NodeSet of all ancestor nodes, ordered from closest to furthest.

```ruby
node.ancestors
```

--------------------------------

### Get Node Line Number

Source: https://github.com/sparklemotion/nokogiri/wiki/Cheat-sheet

Retrieves the line number where this node appeared in the input source.

```ruby
node.line
```

--------------------------------

### Get Matching Ancestor Nodes

Source: https://github.com/sparklemotion/nokogiri/wiki/Cheat-sheet

Returns a NodeSet of ancestor nodes that match the given selector.

```ruby
node.ancestors(selector)
```

--------------------------------

### Stuff Ruby Objects into Johnson Context and Evaluate

Source: https://github.com/sparklemotion/nokogiri/blob/main/test/files/tlm.html

Illustrates how to define a Ruby object and make it available within the JavaScript context, then evaluate JavaScript that uses it.

```ruby
A = Struct.new(:foo)

ctx = Johnson::Context.new
ctx['alert'] = lambda { |x| puts x }
ctx['a'] = A.new("bar")
ctx.evaluate('alert(a.foo);')
```

--------------------------------

### Get Node Content

Source: https://github.com/sparklemotion/nokogiri/wiki/Cheat-sheet

Retrieves the text content of a node. Aliases node.text, node.inner_text, and node.to_str.

```ruby
node.content
```

--------------------------------

### Access and Modify Parent and Children

Source: https://github.com/sparklemotion/nokogiri/wiki/Cheat-sheet

Covers how to get the parent of a node, and how to access, replace, or add children.

```ruby
## Parent
node.parent
node.parent=(node)
## Children
node.child # returns a Node
node.children # Get the list of children of this node as a NodeSet
node.children=(node_or_tags)
  # Set the inner html for this Node
  # Returns the reparented node (if +node_or_tags+ is a Node), 
  #   or returns a NodeSet (if +node_or_tags+ is a DocumentFragment, NodeSet, or string).
node.elements # alias: node.element_children # Get the list of child Elements of this node as a NodeSet.
node.add_child(node_or_tags)
  # Add +node_or_tags+ as a child of this Node.
  # Returns the reparented node (if +node_or_tags+ is a Node),

```

--------------------------------

### Run Gumbo HTML5 Parser Tests

Source: https://github.com/sparklemotion/nokogiri/blob/main/CONTRIBUTING.md

Execute the test suite for the gumbo HTML5 parser. Ensure the html5lib-tests submodule is initialized.

```sh
bundle exec rake gumbo
```

--------------------------------

### Configure GC Levels for Testing

Source: https://github.com/sparklemotion/nokogiri/blob/main/CONTRIBUTING.md

Set environment variables to control garbage collection behavior during testing. Options include 'compact', 'verify', and 'stress'.

```sh
NOKOGIRI_TEST_GC_LEVEL=compact bundle exec rake compile test
```

```sh
NOKOGIRI_TEST_GC_LEVEL=verify bundle exec rake compile test
```

```sh
NOKOGIRI_TEST_GC_LEVEL=stress bundle exec rake compile test
```

--------------------------------

### Run Memory Usage Suite

Source: https://github.com/sparklemotion/nokogiri/blob/main/CONTRIBUTING.md

Execute a specific test suite focused on memory usage, analyzing RSS size and using linear interpolation.

```sh
bundle exec rake compile test:memory_suite
```

--------------------------------

### Get Internal Pointer ID

Source: https://github.com/sparklemotion/nokogiri/wiki/Cheat-sheet

Returns the internal pointer number for this node, used for identification within Nokogiri.

```ruby
node.pointer_id
```

--------------------------------

### Compile and Run Tests

Source: https://github.com/sparklemotion/nokogiri/blob/main/CONTRIBUTING.md

Execute the compile and test tasks using Rake. This is the standard way to run the test suite.

```sh
bundle exec rake compile test
```

--------------------------------

### Get Element Description

Source: https://github.com/sparklemotion/nokogiri/wiki/Cheat-sheet

Fetch the Nokogiri::HTML::ElementDescription for the node. Returns nil for XML documents or unknown tags.

```ruby
node.description
```

--------------------------------

### Convert Node to String Representation

Source: https://github.com/sparklemotion/nokogiri/wiki/Cheat-sheet

Get the string representation of a Node. Returns XML if the document is XML, otherwise HTML.

```ruby
node.to_s
```

--------------------------------

### Set video attributes for upload

Source: https://github.com/sparklemotion/nokogiri/blob/main/test/files/tlm.html

Fetch the upload page, fill in the video title, description, category, and keywords, then submit the upload form. The category is represented by a numerical ID.

```ruby
# Set the video attributes  
page = agent.get('http://youtube.com/my_videos_upload')  
form = page.form('theForm')  
form.field_myvideo_title = 'My video title'  
form.field_myvideo_descr = "My video description"  
form.field_myvideo_categories = 28  
form.field_myvideo_keywords = 'my tag'  
page = form.submit(form.buttons.name('action_upload').first)
```

--------------------------------

### Handle Node Attributes

Source: https://github.com/sparklemotion/nokogiri/wiki/Cheat-sheet

Illustrates how to get, set, check for, and delete attributes of a Nokogiri node, treating them like a hash.

```ruby
# Attributes, like a hash that maps string keys to string values
node['src'] # aliases: node.get_attribute, node.attr.
node['src'] = 'value' # alias node.set_attribute
node.key?('src') # alias node.has_attribute?
node.keys
node.values
node.delete('src') # alias of node.remove_attribute
node.each { |attr_name, attr_value| }
```

--------------------------------

### Initialize Nokogiri XML Node

Source: https://github.com/sparklemotion/nokogiri/wiki/Cheat-sheet

Demonstrates two ways to initialize a new XML node within a Nokogiri document.

```ruby
node = Nokogiri::XML::Node.new('name', document) # initialize a new node
node = document.create_element('name') # shortcut
```

--------------------------------

### Upload Video File

Source: https://github.com/sparklemotion/nokogiri/blob/main/test/files/tlm.html

This snippet shows how to set the video file name and submit a form for uploading. It assumes the file name is provided as a command-line argument.

```ruby
# Upload the video  
page = page.form('theForm') { |f|  
  f.file_uploads.name('field_uploadfile').first.file_name = ARGV[0]  
}.submit  
page.body =~ /<textarea[^>]*>(.*)<\/textarea>/m  
puts $1
```

--------------------------------

### Get Default Namespace

Source: https://github.com/sparklemotion/nokogiri/wiki/Cheat-sheet

Returns the default namespace object defined on this node (e.g., from an 'xmlns="..."' attribute).

```ruby
node.namespace
```

--------------------------------

### Configure Parallel Compilation and Testing

Source: https://github.com/sparklemotion/nokogiri/blob/main/CONTRIBUTING.md

Set environment variables NCPU and MAKEFLAGS to enable parallel execution for compilation and testing.

```sh
export NCPU=8
export MAKEFLAGS=-j8
bundle exec rake compile test
```

--------------------------------

### Get Inner HTML

Source: https://github.com/sparklemotion/nokogiri/wiki/Cheat-sheet

Returns the HTML representation of the node's children, joined together. Useful for serializing child nodes.

```ruby
node.inner_html
```

--------------------------------

### Generate Screencast with Brobinius

Source: https://github.com/sparklemotion/nokogiri/blob/main/test/files/tlm.html

Use the --screencast option with Brobinius to automatically create and upload a screencast of your Ruby program to YouTube. The --geoff flag can be added for voice-over by Geoffrey Grosenbach.

```bash
$ brobinius --screencast my_code.rb
```

--------------------------------

### Get Last Element Child Node

Source: https://github.com/sparklemotion/nokogiri/wiki/Cheat-sheet

Retrieves the last child node that is an element. Returns nil if no element children exist.

```ruby
node.last_element_child
```

--------------------------------

### Get First Element Child Node

Source: https://github.com/sparklemotion/nokogiri/wiki/Cheat-sheet

Retrieves the first child node that is an element. Returns nil if no element children exist.

```ruby
node.first_element_child
```

--------------------------------

### Fast Gumbo Development Builds

Source: https://github.com/sparklemotion/nokogiri/blob/main/CONTRIBUTING.md

Enable faster feedback loops for libgumbo development by using a specific rake task for immediate compilation of changed files.

```sh
bundle exec rake clean compile -- --gumbo-dev
# change a gumbo file
bundle exec rake compile # immediate compilation of changed file and relinking of nokogiri.so
```

--------------------------------

### Parsing Basic XML Structure

Source: https://github.com/sparklemotion/nokogiri/blob/main/doc/xml/parsing.md

Demonstrates parsing a simple XML document with nested elements and text content. Shows the resulting document structure.

```ruby
xml = '<root>
  <foo>Two</foo>
  <bar>Four</bar>
</root>'
doc = Nokogiri::XML.parse(xml)
doc
# =>
#(Document: {
  name = "document",
  children = [
    #(Element: {
      name = "root",
      children = [
        #(Text "One"),
        #(Element: {
          name = "foo",
          children = [ #(Text "Two")]
          }),
        #(Text "Three"),
        #(Element: {
          name = "bar",
          children = [ #(Text "Four")]
          }),
        #(Text "Five")]
      })]
  })

```