class Kramdown::Converter::Base

Base class for converters

This class serves as base class for all converters. It provides methods that can/should be used by all converters (like generate_id) as well as common functionality that is automatically applied to the result (for example, embedding the output into a template).

A converter object is used as a throw-away object, i.e. it is only used for storing the needed state information during conversion. Therefore one can't instantiate a converter object directly but only use the Base::convert method.

Implementing a converter

Implementing a new converter is rather easy: just derive a new class from this class and put it in the Kramdown::Converter module (the latter is only needed if auto-detection should work properly). Then you need to implement the convert method which has to contain the conversion code for converting an element and has to return the conversion result.

The actual transformation of the document tree can be done in any way. However, writing one method per element type is a straight forward way to do it - this is how the Html and Latex converters do the transformation.

Have a look at the Base::convert method for additional information!



Can be used by a converter for storing arbitrary information during the conversion process.


The hash with the conversion options.


The root element that is converted.


The warnings array.

Public Class Methods

convert(tree, options = {}) click to toggle source

Convert the element tree tree and return the resulting conversion object (normally a string) and an array with warning messages. The parameter options specifies the conversion options that should be used.

Initializes a new instance of the calling class and then calls the convert method with tree as parameter.

If the template option is specified and non-empty, the template is evaluate with ERB before and/or after the tree conversion depending on the result of apply_template_before? and apply_template_after?. If the template is evaluated before, an empty string is used for the body; if evaluated after, the result is used as body. See ::apply_template.

The template resolution is done in the following way (for the converter ConverterName):

  1. Look in the current working directory for the template.

  2. Append .converter_name (e.g. .html) to the template name and look for the resulting file in the current working directory (the form .convertername is deprecated).

  3. Append .converter_name to the template name and look for it in the kramdown data directory (the form .convertername is deprecated).

  4. Check if the template name starts with 'string://' and if so, strip this prefix away and use the rest as template.

# File lib/kramdown/converter/base.rb, line 100
def self.convert(tree, options = {})
  converter = new(tree, ::Kramdown::Options.merge(options.merge(tree.options[:options] || {})))

  if !converter.options[:template].empty? && converter.apply_template_before?
    apply_template(converter, '')
  result = converter.convert(tree)
  if result.respond_to?(:encode!) && result.encoding != Encoding::BINARY
    result.encode!(tree.options[:encoding] ||
                   (raise ::Kramdown::Error, "Missing encoding option on root element"))
  if !converter.options[:template].empty? && converter.apply_template_after?
    result = apply_template(converter, result)

  [result, converter.warnings]

Public Instance Methods

apply_template_after?() click to toggle source

Returns whether the template should be applied after the conversion of the tree.

Defaults to true.

# File lib/kramdown/converter/base.rb, line 72
def apply_template_after?
apply_template_before?() click to toggle source

Returns whether the template should be applied before the conversion of the tree.

Defaults to false.

# File lib/kramdown/converter/base.rb, line 65
def apply_template_before?
basic_generate_id(str) click to toggle source

The basic version of the ID generator, without any special provisions for empty or unique IDs.

# File lib/kramdown/converter/base.rb, line 236
def basic_generate_id(str)
  gen_id = str.gsub(/^[^a-zA-Z]+/, '')!('^a-zA-Z0-9 -', '')!(' ', '-')
convert(_el) click to toggle source

Convert the element el and return the resulting object.

This is the only method that has to be implemented by sub-classes!

# File lib/kramdown/converter/base.rb, line 121
def convert(_el)
  raise NotImplementedError
extract_code_language(attr) click to toggle source

Extract the code block/span language from the attributes.

# File lib/kramdown/converter/base.rb, line 173
def extract_code_language(attr)
  if attr['class'] && attr['class'] =~ /\blanguage-\S+/
extract_code_language!(attr) click to toggle source

See extract_code_language

Warning: This version will modify the given attributes if a language is present.

# File lib/kramdown/converter/base.rb, line 182
def extract_code_language!(attr)
  lang = extract_code_language(attr)
  attr['class'] = attr['class'].sub(/\blanguage-\S+/, '').strip if lang
  attr.delete('class') if lang && attr['class'].empty?
format_math(el, opts = {}) click to toggle source

Format the given math element with the math engine configured through the option 'math_engine'.

# File lib/kramdown/converter/base.rb, line 205
def format_math(el, opts = {})
  return nil unless @options[:math_engine]

  engine = ::Kramdown::Converter.math_engine(@options[:math_engine])
  if engine, el, opts)
    warning("The configured math engine #{@options[:math_engine]} is not available.")
generate_id(str) click to toggle source

Generate an unique alpha-numeric ID from the the string str for use as a header ID.

Uses the option auto_id_prefix: the value of this option is prepended to every generated ID.

# File lib/kramdown/converter/base.rb, line 221
def generate_id(str)
  str = ::Kramdown::Utils::Unidecoder.decode(str) if @options[:transliterated_header_ids]
  gen_id = basic_generate_id(str)
  gen_id = 'section' if gen_id.empty?
  @used_ids ||= {}
  if @used_ids.key?(gen_id)
    gen_id += "-#{@used_ids[gen_id] += 1}"
    @used_ids[gen_id] = 0
  @options[:auto_id_prefix] + gen_id
highlight_code(text, lang, type, opts = {}) click to toggle source

Highlight the given text in the language lang with the syntax highlighter configured through the option 'syntax_highlighter'.

# File lib/kramdown/converter/base.rb, line 191
def highlight_code(text, lang, type, opts = {})
  return nil unless @options[:syntax_highlighter]

  highlighter = ::Kramdown::Converter.syntax_highlighter(@options[:syntax_highlighter])
  if highlighter, text, lang, type, opts)
    warning("The configured syntax highlighter #{@options[:syntax_highlighter]} is not available.")
in_toc?(el) click to toggle source

Return true if the header element el should be used for the table of contents (as specified by the toc_levels option).

# File lib/kramdown/converter/base.rb, line 161
def in_toc?(el)
  @options[:toc_levels].include?(el.options[:level]) && (el.attr['class'] || '') !~ /\bno_toc\b/
output_header_level(level) click to toggle source

Return the output header level given a level.

Uses the header_offset option for adjusting the header level.

# File lib/kramdown/converter/base.rb, line 168
def output_header_level(level)
  [[level + @options[:header_offset], 6].min, 1].max
smart_quote_entity(el) click to toggle source

Return the entity that represents the given smart_quote element.

# File lib/kramdown/converter/base.rb, line 247
def smart_quote_entity(el)
  res = @options[:smart_quotes][SMART_QUOTE_INDICES[el.value]]
warning(text) click to toggle source

Add the given warning text to the warning array.

# File lib/kramdown/converter/base.rb, line 155
def warning(text)
  @warnings << text