diff --git a/lib/rbmark.rb b/lib/rbmark.rb
index ff28477..5895aea 100644
--- a/lib/rbmark.rb
+++ b/lib/rbmark.rb
@@ -1,55 +1,373 @@
 # frozen_string_literal: true
 
 module RBMark
-  # Parser class
-  class Parser
-    def initialize(variants, default)
-      @default = default
-      @variants = variants
-      @markers = @variants.map { |x| [x.begin, x] }.to_h
-    end
-
-    # Parse text using the given variants
-    # @param text [String]
-    # @return [Array<::RBMark::DOM::DOMObject>]
-    def parse(text)
-      chunks = []
-      until text.nil? or text.empty?
-        before, chunk, text = get_chunk(text)
-        chunks.append(@default.parse(before)) unless before.empty?
-        next unless chunk
-
-        chunks.append(chunk)
+  # Module for representing parsing-related constructs
+  module Parsing
+    # Abstract scanner interface implementation
+    class Scanner
+      def initialize
+        @variants = []
       end
-      chunks.flatten
-    end
 
-    private
-
-    def get_chunk(text)
-      element, match = get_element(text)
-      if element
-        chunk, after = finalize_element(text[match.offset(0)[0]..], element)
-        return [match.pre_match, chunk, after] if chunk
-
-        return [match.pre_match, nil, match.post_match]
+      # Scan text
+      # @param text [String]
+      # @return [Array<RBMark::DOM::DOMObject>]
+      def scan(_text)
+        raise StandardError, "Abstract method called"
+        # ...
       end
-      [text, nil, nil]
+
+      attr_accessor :variants
     end
 
-    def get_element(text)
-      @markers.filter_map do |marker|
-        [marker[1], text.match(marker[0])] if text.match(marker[0])
-      end.min_by { |x| x[1].offset(0)[0] }
+    # Line-level scanner for blocks
+    class LineScanner < Scanner
+      # (see ::RBMark::Parsing::Scanner#scan)
+      def scan(text, buffer: "", blocks: [], mode: nil)
+        prepare
+        lines = text.lines
+        lines.each_with_index do |line, index|
+          buffer += line
+          ahead = lines.fetch(index + 1, nil)
+          blocks, buffer, mode = try_begin(line,
+                                           blocks,
+                                           buffer,
+                                           mode,
+                                           lookahead: ahead)
+          if mode&.end?(line, lookahead: ahead, blocks: blocks, buffer: buffer)
+            blocks, buffer, mode = flush(blocks, buffer, mode)
+          end
+        end
+        flush(blocks, buffer, mode)[0]
+      end
+
+      # Predict mode for given line
+      # @param line [String]
+      # @return [Object]
+      def select_mode(line, **message)
+        @variants.find do |variant|
+          variant[0].begin?(line, **message)
+        end&.at(0)
+      end
+
+      private
+
+      # Attempt to open a new mode and, if possible, call :begin to prepare the block
+      def try_begin(line, blocks, buffer, mode, lookahead: nil)
+        return blocks, buffer, mode if mode
+
+        mode = select_mode(line, lookahead: lookahead,
+                                 blocks: blocks,
+                                 buffer: buffer)
+        blocks.append(mode.begin(line)) if mode.respond_to?(:begin)
+        [blocks, buffer, mode]
+      end
+
+      # Assign self as parent to all variants
+      # @return [void]
+      def prepare
+        @variants.each do |variant|
+          unless variant[0].is_a? ::RBMark::Parsing::BlockVariant
+            raise StandardError, "#{variant} is not a BlockVariant"
+          end
+
+          variant[0].parent = self
+        end
+        @variants.sort_by!(&:last)
+      end
+
+      # Flush the buffer using given mode
+      # @param blocks [Array<RBMark::DOM::DOMObject>]
+      # @param buffer [String]
+      # @param mode [Object]
+      # @return [Array(Array<RBMark::DOM::DOMObject>, String, ::RBMark::Parsing::Variant)]
+      def flush(blocks, buffer, mode)
+        return blocks, "" if buffer == ""
+
+        mode.end(blocks.last, buffer) if mode.respond_to?(:end)
+        blocks.append(mode.flush(buffer)) if mode.respond_to?(:flush)
+        if mode.respond_to?(:restructure)
+          blocks, buffer, mode = mode.restructure(blocks, buffer, mode)
+        else
+          buffer = ""
+          mode = nil
+        end
+        [blocks, buffer, mode]
+      end
     end
 
-    def finalize_element(text, element)
-      match = text.match(element.end)
-      return nil, nil unless match
+    # Abstract variant interface
+    class Variant
+    end
 
-      chunk_text = text[..(match.offset(0)[1] - 1)]
-      remaining_text = text[match.offset(0)[1]..]
-      [element.parse(chunk_text), remaining_text]
+    # Abstract block-level variant
+    class BlockVariant < Variant
+      # Check if a block begins on this line
+      # @param line [String]
+      # @param opts [Hash] options hash
+      # @option [String, nil] :lookahead next line over
+      # @option [Array<::RBMark::Parsing::BlockVariant>] :blocks current list of blocks
+      # @option [String] :buffer current state of buffer
+      # @return [Boolean]
+      def begin?(_line, **_opts)
+        raise StandardError, "Abstract method called"
+      end
+
+      # Check if a block ends on this line
+      # @param line [String]
+      # @param opts [Hash] options hash
+      # @option [String, nil] :lookahead next line over
+      # @option [Array<::RBMark::Parsing::BlockVariant>] :blocks current list of blocks
+      # @option [String] :buffer current state of buffer
+      # @return [Boolean]
+      def end?(_line, **_opts)
+        raise StandardError, "Abstract method called"
+      end
+
+      # @!method begin(buffer)
+      #   Open a block to be later filled in by BlockVariant#end
+      #   @param buffer [String]
+      #   @return [::RBMark::DOM::DOMObject]
+
+      # @!method end(block, buffer)
+      #   Finalize a block opened by begin
+      #   @param buffer [String]
+      #   @return [void]
+
+      # @!method flush(buffer)
+      #   Flush buffer and create a new DOM object
+      #   @param buffer [String]
+      #   @return [::RBMark::DOM::DOMObject]
+
+      # @!method restructure(blocks, buffer, mode)
+      #   Restructure current set of blocks (if method is defined)
+      #   @param blocks [Array<::RBMark::DOM::DOMObject>]
+      #   @param buffer [String]
+      #   @param mode [::RBMark::Parsing::Variant]
+      #   @return [Array(Array<RBMark::DOM::DOMObject>, String, ::RBMark::Parsing::Variant)]
+
+      attr_accessor :parent
+    end
+
+    # Paragraph breaking variant
+    class BreakerVariant < BlockVariant
+      # Check that a paragraph matches the breaker
+      # @param buffer [String]
+      # @return [Class, nil]
+      def match(_buffer)
+        raise StandardError, "Abstract method called"
+      end
+
+      # @!method preprocess(buffer)
+      #   preprocess buffer
+      #   @param buffer [String]
+      #   @return [String]
+    end
+
+    # Paragraph variant
+    class ParagraphVariant < BlockVariant
+      # (see BlockVariant#begin?)
+      def begin?(line, **_opts)
+        line.match?(/\S/)
+      end
+
+      # (see BlockVariant#end?)
+      def end?(line, lookahead: nil, **_opts)
+        return true if check_paragraph_breakers(line)
+
+        if lookahead
+          return false if check_paragraph_breakers(lookahead)
+
+          return false if lookahead.match(/^ {4}/)
+
+          !parent.select_mode(lookahead).is_a?(self.class)
+        else
+          true
+        end
+      end
+
+      # (see BlockVariant#flush)
+      # @sg-ignore
+      def flush(buffer)
+        dom_class = nil
+        breaker = parent.variants.find do |x|
+          x[0].is_a?(::RBMark::Parsing::BreakerVariant) &&
+            (dom_class = x[0].match(buffer))
+        end&.first
+        buffer = breaker.preprocess(buffer) if breaker.respond_to?(:preprocess)
+        (dom_class or ::RBMark::DOM::Paragraph).parse(buffer.strip)
+      end
+
+      private
+
+      def check_paragraph_breakers(line)
+        breakers = parent.variants.filter_map do |x|
+          x[0] if x[0].is_a? ::RBMark::Parsing::BreakerVariant
+        end
+        breakers.any? { |x| x.begin?(line, breaks_paragraph: true) }
+      end
+    end
+
+    # Thematic break variant
+    class ThematicBreakVariant < BlockVariant
+      # (see BlockVariant#begin?)
+      def begin?(line, **_opts)
+        line.match?(/^(?:[- ]{3,}|[_ ]{3,}|[* ]{3,})$/) &&
+          line.match?(/^ {0,3}[-_*]/) &&
+          (
+            line.count("-") >= 3 ||
+            line.count("_") >= 3 ||
+            line.count("*") >= 3
+          )
+      end
+
+      # (see BlockVariant#end?)
+      def end?(_line, **_opts)
+        true
+      end
+
+      # (see BlockVariant#flush)
+      def flush(_buffer)
+        ::RBMark::DOM::HorizontalRule.new
+      end
+    end
+
+    # ATX Heading variant
+    class ATXHeadingVariant < BlockVariant
+      # (see BlockVariant#begin?)
+      def begin?(line, **_opts)
+        line.match?(/^ {0,3}\#{1,6}(?: .*|)$/)
+      end
+
+      # (see BlockVariant#end?)
+      def end?(_line, **_opts)
+        true
+      end
+
+      # (see BlockVariant#flush)
+      def flush(buffer)
+        lvl, content = buffer.match(/^ {0,3}(\#{1,6})( .*|)$/)[1..2]
+        content = content.gsub(/( #+|)$/, "")
+        heading(lvl).parse(content.strip)
+      end
+
+      private
+
+      def heading(lvl)
+        case lvl.length
+        when 1 then ::RBMark::DOM::Heading1
+        when 2 then ::RBMark::DOM::Heading2
+        when 3 then ::RBMark::DOM::Heading3
+        when 4 then ::RBMark::DOM::Heading4
+        when 5 then ::RBMark::DOM::Heading5
+        when 6 then ::RBMark::DOM::Heading6
+        end
+      end
+    end
+
+    # Paragraph closing variant
+    class BlankSeparator < BreakerVariant
+      # (see BlockVariant#begin?)
+      def begin?(line, breaks_paragraph: nil, **_opts)
+        breaks_paragraph &&
+          line.match?(/^ {0,3}$/)
+      end
+
+      # (see BlockVariant#end?)
+      def end?(_line, **_opts)
+        true
+      end
+
+      # (see BreakerVariant#match)
+      def match(_buffer)
+        nil
+      end
+    end
+
+    # Setext heading variant
+    class SetextHeadingVariant < BreakerVariant
+      # (see BlockVariant#begin?)
+      def begin?(line, breaks_paragraph: nil, **_opts)
+        breaks_paragraph &&
+          line.match?(/^ {0,3}(?:-+|=+) *$/)
+      end
+
+      # (see BlockVariant#end?)
+      def end?(_line, **_opts)
+        true
+      end
+
+      # (see BreakerVariant#match)
+      def match(buffer)
+        return nil unless preprocess(buffer).match(/\S/)
+
+        heading(buffer.lines.last)
+      end
+
+      # (see BreakerVariant#preprocess)
+      def preprocess(buffer)
+        buffer.lines[..-2].join
+      end
+
+      private
+
+      def heading(buffer)
+        case buffer
+        when /^ {0,3}-+ *$/ then ::RBMark::DOM::Heading2
+        when /^ {0,3}=+ *$/ then ::RBMark::DOM::Heading1
+        end
+      end
+    end
+
+    # Indented literal block variant
+    class IndentedBlockVariant < BlockVariant
+      # (see BlockVariant#begin?)
+      def begin?(line, **_opts)
+        line.match?(/^(?: {4}|\t)/)
+      end
+
+      # (see BlockVariant#end?)
+      def end?(_line, lookahead: nil, **_opts)
+        !lookahead&.match?(/^(?: {4}.*|\s*|\t)$/)
+      end
+
+      # (see BlockVariant#flush)
+      def flush(buffer)
+        text = buffer.lines.map { |x| "#{x.chomp[4..]}\n" }.join
+        block = ::RBMark::DOM::IndentBlock.new
+        block.content = text # TODO: replace this with inline text
+        block
+      end
+    end
+
+    # Fenced code block
+    class FencedCodeBlock < BlockVariant
+      # (see BlockVariant#begin?)
+      def begin?(line, **_opts)
+        line.match?(/^(?:`{3,}[^`]*|~{3,}.*)$/)
+      end
+
+      # (see BlockVariant#end?)
+      def end?(line, blocks: nil, buffer: nil, **_opts)
+        buffer.lines.length > 1 and
+          line.strip == blocks.last.properties[:expected_closer]
+      end
+
+      # (see BlockVariant#begin)
+      def begin(buffer)
+        block = ::RBMark::DOM::CodeBlock.new
+        block.properties[:expected_closer] = buffer.match(/^(?:`{3,}|~{3,})/)[0]
+        block.properties[:infostring] = buffer.match(/^(?:`{3,}|~{3,})(.*)$/)[1]
+                                              .strip
+        block
+      end
+
+      # (see BlockVariant#end)
+      def end(block, buffer)
+        # TODO: replace this with inline text
+        block.properties.delete(:expected_closer)
+        block.content = buffer.lines[1..-2].join
+      end
     end
   end
 
@@ -66,42 +384,56 @@ module RBMark
           @subclasses.append(subclass)
           subclass.variants = @variants.dup
           subclass.variants ||= []
-          subclass.default_class = @default_class
+          subclass.atomic_mode = @atomic_mode
+          subclass.scanner_class = @scanner_class
         end
 
         # Add potential sub-element variant
         # @param cls [Class] DOMObject subclass
-        def variant(cls)
-          unless cls < ::RBMark::DOM::DOMObject
+        def variant(cls, prio: 1)
+          unless cls < ::RBMark::Parsing::Variant
             raise StandardError, "#{cls} is not a DOMObject subclass"
           end
 
-          @variants.append(cls)
+          @variants.append([cls, prio])
           @subclasses&.each do |subclass|
-            subclass.variant(cls)
+            subclass.variant(cls, prio)
           end
         end
 
-        # Set default element class
+        # Set scanner class
         # @param cls [Class] DOMObject subclass
-        def default(cls)
-          unless cls < ::RBMark::DOM::DOMObject
-            raise StandardError, "#{cls} is not a DOMObject subclass"
+        def scanner(cls)
+          unless cls < ::RBMark::Parsing::Scanner
+            raise StandardError, "#{cls} is not a Scanner subclass"
           end
 
-          @default_class = cls
+          @scanner_class = cls
           @subclasses&.each do |subclass|
-            subclass.default(cls)
+            subclass.scanner(cls)
           end
         end
 
+        # Prepare scanner and variants
+        # @return [void]
+        def prepare
+          return if @prepared
+
+          @scanner = @scanner_class.new
+          @scanner.variants = @variants.map { |x| [x[0].new, x[1]] }
+        end
+
         # Parse text from the given context
         # @param text [String]
         # @return [self]
         def parse(text)
-          parser = ::RBMark::Parser.new(@variants, @default_class)
-          instance = create
-          instance.append(*parser.parse(text))
+          prepare unless @atomic_mode
+          instance = new
+          if @atomic_mode
+            instance.content = text
+          else
+            instance.append(*@scanner.scan(text))
+          end
           instance
         end
 
@@ -115,7 +447,13 @@ module RBMark
           end
         end
 
-        attr_accessor :variants, :begin, :end, :default_class, :alt_for
+        # Set the atomic flag
+        # @return [void]
+        def atomic
+          @atomic_mode = true
+        end
+
+        attr_accessor :variants, :scanner_class, :alt_for, :atomic_mode
       end
 
       def initialize
@@ -169,12 +507,6 @@ module RBMark
         @content = text
       end
 
-      # Get length of text contents
-      # @return [Integer]
-      def length
-        @children.map(&:length).sum
-      end
-
       # Get text content of a DOMObject
       # @return [String, nil]
       attr_reader :content, :children, :properties
@@ -182,350 +514,96 @@ module RBMark
 
     # Inline text
     class Text < DOMObject
-      # Stub parser for inline text element
-      # @param text [String]
-      # @return [self]
-      def self.parse(text)
-        instance = new
-        instance.content = text.gsub("\n", ' ').gsub(/\s+/, " ")
-        instance
-      end
-
-      # Get length of inline text
-      # @return [Integer]
-      def length
-        @content.length
-      end
     end
 
     # Inline preformatted text
     class InlinePre < DOMObject
-      self.begin = /(?<!\\)`(?!`)/
-      self.end = /`.+?`/
-
-      # Stub parser for inline text element
-      # @param text [String]
-      # @return [self]
-      def self.parse(text)
-        instance = new
-        element = ::RBMark::DOM::Text.new
-        element.content = text
-        instance.append element
-        instance
-      end
-
-      # Get length of inline preformatted text
-      # @return [Integer]
-      def length
-        @content ? @content.length : 0
-      end
     end
 
     # Infline formattable text
     class InlineFormattable < DOMObject
-      # (see ::RBMark::DOM::DOMObject.parse)
-      def self.parse(text)
-        cleanup(super(text))
-      end
-
-      # Clean up internal text chunks
-      def self.cleanup(paragraph)
-        previous = nil
-        delete = []
-        paragraph.children.each_with_index do |child, index|
-          if previous.nil? || previous.is_a?(::RBMark::DOM::InlineBreak)
-            if child.is_a? ::RBMark::DOM::Text
-              child.content = child.content.lstrip
-            end
-            delete.append(index) if child.is_a? ::RBMark::DOM::InlineBreak
-          end
-          previous = child
-        end
-        delete.reverse_each do |index|
-          paragraph.delete_at(index)
-        end
-        paragraph
-      end
+      atomic
     end
 
     # Bold text
     class InlineBold < InlineFormattable
-      self.begin = /(?<!\\)\*\*(?!\*\*)/
-      self.end = /\*\*.+?\*\*/
-
-      # (see ::RBMark::DOM::DOMObject.parse)
-      def self.parse(text)
-        super(text[2..-3])
-      end
     end
 
     # Italics text
     class InlineItalics < InlineFormattable
-      self.begin = /(?<!\\)\*(?!\*)/
-      self.end = /\*.+?\*/
-
-      # (see ::RBMark::DOM::DOMObject.parse)
-      def self.parse(text)
-        super(text[1..-2])
-      end
     end
 
     # Inline italics text (alternative)
     class InlineAltItalics < InlineFormattable
-      self.begin = /(?<!\\)_(?!_)/
-      self.end = /_.+?_/
-      self.alt_for = ::RBMark::DOM::InlineItalics
-
-      # (see ::RBMark::DOM::DOMObject.parse)
-      def self.parse(text)
-        super(text[1..-2])
-      end
     end
 
     # Underline text
     class InlineUnder < InlineFormattable
-      self.begin = /(?<!\\)__(?!__)/
-      self.end = /__.+?__/
-
-      # (see ::RBMark::DOM::DOMObject.parse)
-      def self.parse(text)
-        super(text[2..-3])
-      end
     end
 
     # Strikethrough text
     class InlineStrike < InlineFormattable
-      self.begin = /(?<!\\)~~(?!~~)/
-      self.end = /~~.+?~~/
-
-      # (see ::RBMark::DOM::DOMObject.parse)
-      def self.parse(text)
-        super(text[2..-3])
-      end
     end
 
     # Hyperreferenced text
     class InlineLink < InlineFormattable
-      self.begin = /(?<![!\\])\[[^\]]+?\]\([^)]+?\)/
-      self.end = self.begin
-
-      # (see ::RBMark::DOM::DOMObject.parse)
-      def self.parse(text)
-        text, link = text.match(/\[([^\]]+?)\]\(([^)]+?)\)/)[1..2]
-        instance = super(text)
-        instance.property link: link
-        instance
-      end
     end
 
     # Image
     class InlineImage < InlinePre
-      self.begin = /(?<!\\)!\[[^\]]+?\]\([^)]+?\)/
-      self.end = self.begin
-
-      # (see ::RBMark::DOM::DOMObject.parse)
-      def self.parse(text)
-        text, link = text.match(/!\[([^\]]+?)\]\(([^)]+?)\)/)[1..2]
-        instance = super(text)
-        instance.property link: link
-        instance
-      end
     end
 
     # Linebreak
     class InlineBreak < DOMObject
-      self.begin = /  /
-      self.end = /  /
-
-      # (see ::RBMark::DOM::DOMObject.parse)
-      def self.parse(_text)
-        new
-      end
-
-      # Stub for inline break length
-      def length
-        0
-      end
     end
 
     # Document root
     class Document < DOMObject
-      # (see ::RBMark::DOM::DOMObject.parse)
-      def self.parse(text)
-        merge(vacuum(super(normalize_newlines(text))))
-      end
-
-      # Replace all forms of line endings with UNIX format newline
-      def self.normalize_newlines(text)
-        text.gsub(/(?:\r\n|\n\r|\r|\n)/, "\n")
-      end
-
-      # Remove all elements with absolute lenght of 0
-      def self.vacuum(document)
-        delete = []
-        document.children.each_with_index do |element, index|
-          delete.append(index) unless element.length.positive?
-        end
-        delete.reverse_each do |index|
-          document.delete_at(index)
-        end
-        document
-      end
-
-      # Merge adjacent lists with indent blocks as per markdownguide guidelines
-      def self.merge(document)
-        last_list = nil
-        delete_deferred = []
-        document.children.each_with_index do |child, index|
-          if !last_list and [::RBMark::DOM::ULBlock,
-                             ::RBMark::DOM::OLBlock].include? child.class
-            last_list = child
-          elsif last_list and mergeable?(last_list, child)
-            merge_adjacent(last_list, child)
-            delete_deferred.append(index)
-          else
-            last_list = nil
-          end
-        end
-        delete_deferred.reverse_each { |index| document.delete_at(index) }
-        document
-      end
-
-      # Check if 2 elements can be merged
-      def self.mergeable?(list, child)
-        if child.is_a? ::RBMark::DOM::IndentBlock or
-           (child.is_a? ::RBMark::DOM::ULBlock and
-            list.is_a? ::RBMark::DOM::ULBlock) or
-           (child.is_a? ::RBMark::DOM::OLBlock and
-            list.is_a? ::RBMark::DOM::OLBlock and
-            child.children.first.properties[:number] >
-            list.children.last.properties[:number])
-          true
-        else
-          false
-        end
-      end
-
-      # Merge 2 elements
-      def self.merge_adjacent(left, right)
-        if right.is_a? ::RBMark::DOM::ULBlock or
-           right.is_a? ::RBMark::DOM::OLBlock
-          right.children.each do |child|
-            left.append(child)
-          end
-        elsif right.is_a? ::RBMark::DOM::IndentBlock
-          left.children.last.append(
-            *::RBMark::DOM::ListElement.parse(right.children.first.content)
-                                       .children
-          )
-        end
-      end
+      scanner ::RBMark::Parsing::LineScanner
+      variant ::RBMark::Parsing::ATXHeadingVariant
+      variant ::RBMark::Parsing::ThematicBreakVariant
+      variant ::RBMark::Parsing::SetextHeadingVariant
+      variant ::RBMark::Parsing::IndentedBlockVariant
+      variant ::RBMark::Parsing::FencedCodeBlock
+      variant ::RBMark::Parsing::BlankSeparator, prio: 9998
+      variant ::RBMark::Parsing::ParagraphVariant, prio: 9999
     end
 
     # Paragraph in a document (separated by 2 newlines)
     class Paragraph < InlineFormattable
-      # (see ::RBMark::DOM::DOMObject.parse)
-      # @return [Array<self>]
-      def self.parse(text)
-        text.split("\n\n").map do |chunk|
-          super(chunk)
-        end
-      end
+      atomic
     end
 
     # Heading level 1
     class Heading1 < InlineFormattable
-      self.begin = /^# /
-      self.end = /#?$/
-
-      # (see ::RBMark::DOM::DOMObject.parse)
-      def self.parse(text)
-        super(text.gsub(self.begin, '').gsub(self.end, ''))
-      end
     end
 
     # Heading level 2
     class Heading2 < Heading1
-      self.begin = /^## /
-      self.end = /(?:##)?$/
     end
 
     # Heading level 3
     class Heading3 < Heading1
-      self.begin = /^### /
-      self.end = /(?:###)?$/
     end
 
     # Heading level 4
     class Heading4 < Heading1
-      self.begin = /^#### /
-      self.end = /(?:####)?$/
     end
 
     # Heading level 5
     class Heading5 < Heading1
-      self.begin = /^##### /
-      self.end = /(?:#####)?$/
     end
 
     # Heading level 6
     class Heading6 < Heading1
-      self.begin = /^###### /
-      self.end = /(?:######)?$/
-    end
-
-    # Alternative heading 1
-    class AltHeading1 < InlineFormattable
-      self.begin = /^[^\n]+\n={3,}$/m
-      self.end = /={3,}$/
-      self.alt_for = ::RBMark::DOM::Heading1
-
-      # (see ::RBMark::DOM::DOMObject.parse)
-      def self.parse(text)
-        super(text.match(/\A[^\n]+$/)[0].strip)
-      end
-    end
-
-    # Alternative heading 2
-    class AltHeading2 < InlineFormattable
-      self.begin = /^[^\n]+\n-{3,}$/m
-      self.end = /-{3,}$/
-      self.alt_for = ::RBMark::DOM::Heading2
-
-      # (see ::RBMark::DOM::DOMObject.parse)
-      def self.parse(text)
-        super(text.match(/\A[^\n]+$/)[0].strip)
-      end
     end
 
     # Preformatted code block
     class CodeBlock < DOMObject
-      self.begin = /^```[^\n]*$/
-      self.end = /^```[^\n]*\n.*?\n```$/m
-
-      # Stub parser for block text element
-      # @param text [String]
-      # @return [self]
-      def self.parse(text)
-        instance = new
-        language = text.match(/\A```([^\n]*)/)[1].strip
-        element = ::RBMark::DOM::Text.new
-        element.content = text.lines[1..-2].join('').rstrip
-        instance.append(element)
-        instance.property language: language
-        instance
-      end
     end
 
     # Quote block
     class QuoteBlock < Document
-      self.begin = /^> \S/
-      self.end = /(?:^(?!>)|\Z)/
-
-      # stub
-      def self.parse(text)
-        super(text.lines.map { |x| x[2..] }.join(''))
-      end
     end
 
     # Table
@@ -538,122 +616,19 @@ module RBMark
 
     # Unordered list
     class ULBlock < DOMObject
-      self.begin = /^- +\S+/
-      self.end = /(?:^(?!- +\S+|  )|\Z)/
-
-      # (see RBMark::DOM::DOMObject.parse)
-      def self.parse(text)
-        block = []
-        instance = new
-        text.lines.each do |line|
-          if line.start_with?("- ")
-            unless block.empty?
-              instance.append(::RBMark::DOM::ListElement.parse(block.join('')))
-            end
-            block = [line[2..]]
-          else
-            block.append(line[2..])
-          end
-        end
-        instance.append(::RBMark::DOM::ListElement.parse(block.join('')))
-        instance
-      end
     end
 
     # Ordered list block
     class OLBlock < DOMObject
-      self.begin = /^\d+\. +\S+/
-      self.end = /(?:^(?!\d+\. +\S+| {4})|\Z)/
-
-      # (see RBMark::DOM::DOMObject.parse)
-      def self.parse(text)
-        block = []
-        instance = new
-        counter = nil
-        text.lines.each do |line|
-          if line.start_with?(/^\d+\. /)
-            unless block.empty?
-              instance.append(element(block.join(''), counter))
-            end
-            counter = line.match(/^(\d+)\. /)[1]
-            block = [line.gsub(/^(?:\d+\. | {4})/, '')]
-          else
-            block.append(line.gsub(/^(?:\d+\. | {4})/, ''))
-          end
-        end
-        instance.append(element(block.join(''), counter))
-        instance
-      end
-
-      # Construct a new ListElement
-      def self.element(text, counter)
-        instance = ::RBMark::DOM::ListElement.parse(text)
-        instance.property number: counter
-        instance
-      end
     end
 
     # Indent block
     class IndentBlock < DOMObject
-      self.begin = /^ {4}/
-      self.end = /(?:^(?! {4})|\Z)/
-
-      # (see RBMark::DOM::DOMObject.parse)
-      def self.parse(text)
-        instance = new
-        element = ::RBMark::DOM::Text.new
-        element.content = text.lines.map { |x| x[4..] }.join('')
-        instance.append(element)
-        instance
-      end
     end
 
     # Horizontal rule
     class HorizontalRule < DOMObject
-      self.begin = /^-{3,}$/
-      self.end = /$/
-
-      # stub for HR
-      def self.parse(_text)
-        new
-      end
-
-      # Stub for HR length
-      # @return [Integer]
-      def length
-        1
-      end
-    end
-
-    InlineFormattable.class_exec do
-      default ::RBMark::DOM::Text
-      variant ::RBMark::DOM::InlineBold
-      variant ::RBMark::DOM::InlineItalics
-      variant ::RBMark::DOM::InlineAltItalics
-      variant ::RBMark::DOM::InlineUnder
-      variant ::RBMark::DOM::InlineImage
-      variant ::RBMark::DOM::InlineLink
-      variant ::RBMark::DOM::InlinePre
-      variant ::RBMark::DOM::InlineStrike
-      variant ::RBMark::DOM::InlineBreak
-    end
-
-    Document.class_exec do
-      default ::RBMark::DOM::Paragraph
-      variant ::RBMark::DOM::Heading1
-      variant ::RBMark::DOM::Heading2
-      variant ::RBMark::DOM::Heading3
-      variant ::RBMark::DOM::Heading4
-      variant ::RBMark::DOM::Heading5
-      variant ::RBMark::DOM::Heading6
-      variant ::RBMark::DOM::AltHeading1
-      variant ::RBMark::DOM::AltHeading2
-      variant ::RBMark::DOM::QuoteBlock
-      variant ::RBMark::DOM::CodeBlock
-      variant ::RBMark::DOM::ULBlock
-      variant ::RBMark::DOM::OLBlock
-      variant ::RBMark::DOM::IndentBlock
-      variant ::RBMark::DOM::HorizontalRule
+      atomic
     end
   end
 end
diff --git a/lib/rbmark/renderers.rb b/lib/rbmark/renderers.rb
new file mode 100644
index 0000000..7cbe4b5
--- /dev/null
+++ b/lib/rbmark/renderers.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+module RBMark
+  # Renderers from Markdown to expected output format
+  module Renderers
+  end
+end
+
+require_relative 'renderers/html'
diff --git a/lib/rbmark/renderers/html.rb b/lib/rbmark/renderers/html.rb
new file mode 100644
index 0000000..de8dd2c
--- /dev/null
+++ b/lib/rbmark/renderers/html.rb
@@ -0,0 +1,132 @@
+# frozen_string_literal: true
+
+require 'rbmark'
+
+module RBMark
+  module Renderers
+    # HTML Renderer
+    class HTML
+      ELEMENT_MAP = {
+        "RBMark::DOM::InlinePre" => {
+          tag: "code",
+          inline: true
+        },
+        "RBMark::DOM::InlineBreak" => {
+          tag: "br",
+          inline: true
+        },
+        "RBMark::DOM::InlineBold" => {
+          tag: "strong",
+          inline: true
+        },
+        "RBMark::DOM::InlineItalics" => {
+          tag: "em",
+          inline: true
+        },
+        "RBMark::DOM::InlineUnder" => {
+          tag: "span",
+          inline: true,
+          style: "text-decoration: underline;"
+        },
+        "RBMark::DOM::InlineStrike" => {
+          tag: "s",
+          inline: true
+        },
+        "RBMark::DOM::InlineLink" => {
+          tag: "link",
+          href: true,
+          inline: true
+        },
+        "RBMark::DOM::InlineImage" => {
+          tag: "img",
+          src: true,
+          inline: true
+        },
+        "RBMark::DOM::ULBlock" => {
+          tag: "ul"
+        },
+        "RBMark::DOM::OLBlock" => {
+          tag: "ol"
+        },
+        "RBMark::DOM::IndentBlock" => {
+          tag: "pre"
+        },
+        "RBMark::DOM::ListElement" => {
+          tag: "li"
+        },
+        "RBMark::DOM::Paragraph" => {
+          tag: "p"
+        },
+        "RBMark::DOM::Heading1" => {
+          tag: "h1"
+        },
+        "RBMark::DOM::Heading2" => {
+          tag: "h2"
+        },
+        "RBMark::DOM::Heading3" => {
+          tag: "h3"
+        },
+        "RBMark::DOM::Heading4" => {
+          tag: "h4"
+        },
+        "RBMark::DOM::Heading5" => {
+          tag: "h5"
+        },
+        "RBMark::DOM::Heading6" => {
+          tag: "h6"
+        },
+        "RBMark::DOM::Document" => {
+          tag: "main"
+        },
+        "RBMark::DOM::CodeBlock" => {
+          tag: "pre",
+          outer: {
+            tag: "code"
+          }
+        },
+        "RBMark::DOM::QuoteBlock" => {
+          tag: "blockquote"
+        },
+        "RBMark::DOM::HorizontalRule" => {
+          tag: "hr"
+        },
+        "RBMark::DOM::Text" => nil
+      }.freeze
+
+      def initialize(dom, options)
+        @document = dom
+        @options = options
+      end
+
+      # Render document to HTML
+      def render
+        preambule if @options['preambule']
+        _render(@document, indent = 2)
+        postambule if @options['postambule']
+      end
+
+      private
+
+      def _render(element, indent = 0)
+        
+
+      def preambule
+        @options['preambule'] or <<~TEXT
+        <!DOCTYPE HTML>
+        <html>
+          <head>
+            #{@document['head']}
+          </head>
+          <body>
+        TEXT
+      end
+
+      def postambule
+        @options['postambule'] or <<~TEXT
+          </body>
+        </html>
+        TEXT
+      end    
+    end
+  end
+end
diff --git a/test/test_atx_headers.rb b/test/test_atx_headers.rb
new file mode 100644
index 0000000..58a038a
--- /dev/null
+++ b/test/test_atx_headers.rb
@@ -0,0 +1,102 @@
+# frozen_string_literal: true
+
+require 'minitest/autorun'
+require_relative '../lib/rbmark'
+
+# Test ATX Heading parsing compliance with CommonMark v0.31.2
+class TestATXHeadings < Minitest::Test
+  def test_simple_heading1
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      # ATX Heading level 1
+      Paragraph
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[0])
+  end
+
+  def test_simple_heading2
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      ## ATX Heading level 2
+      Paragraph
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading2, doc.children[0])
+  end
+
+  def test_simple_heading3
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      ### ATX Heading level 3
+      Paragraph
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading3, doc.children[0])
+  end
+
+  def test_simple_heading4
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      #### ATX Heading level 4
+      Paragraph
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading4, doc.children[0])
+  end
+
+  def test_simple_heading5
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      ##### ATX Heading level 5
+      Paragraph
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading5, doc.children[0])
+  end
+
+  def test_simple_heading6
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      ###### ATX Heading level 6
+      Paragraph
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading6, doc.children[0])
+  end
+
+  def test_simple_not_a_heading
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      ####### NOT a heading
+    DOC
+    assert_instance_of(::RBMark::DOM::Paragraph, doc.children[0])
+  end
+
+  def test_breaking_paragrpah
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      Paragraph 1
+      # ATX Heading level 1
+      Paragraph 2
+    DOC
+    assert_instance_of(::RBMark::DOM::Paragraph, doc.children[0])
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[1])
+    assert_instance_of(::RBMark::DOM::Paragraph, doc.children[2])
+  end
+
+  def test_heading_sans_space
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      #NOT an ATX heading
+    DOC
+    assert_instance_of(::RBMark::DOM::Paragraph, doc.children[0])
+  end
+
+  def test_heading_escaped
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      \\# Escaped ATX heading
+    DOC
+    assert_instance_of(::RBMark::DOM::Paragraph, doc.children[0])
+  end
+
+  def test_spaces
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      #### Heading level 4
+       ### Heading level 3
+        ## Heading level 2
+         # Heading level 1
+          # NOT a heading
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading4, doc.children[0])
+    assert_instance_of(::RBMark::DOM::Heading3, doc.children[1])
+    assert_instance_of(::RBMark::DOM::Heading2, doc.children[2])
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[3])
+    refute_instance_of(::RBMark::DOM::Heading1, doc.children[4])
+  end
+end
diff --git a/test/test_fenced_code_block.rb b/test/test_fenced_code_block.rb
new file mode 100644
index 0000000..2d1878b
--- /dev/null
+++ b/test/test_fenced_code_block.rb
@@ -0,0 +1,147 @@
+# frozen_string_literal: true
+
+require 'minitest/autorun'
+require_relative '../lib/rbmark'
+
+# Test Setext Heading parsing compliance with CommonMark v0.31.2
+class TestSetextHeadings < Minitest::Test
+  def test_simple_heading1
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      Foo *bar*
+      =========
+
+      Foo *bar*
+      ---------
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[0])
+    assert_instance_of(::RBMark::DOM::Heading2, doc.children[1])
+  end
+
+  def test_multiline_span
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      Foo *bar
+      baz*
+      ====
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[0])
+    assert_equal(1, doc.children.length)
+  end
+
+  def test_span_inlining
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      start
+
+        Foo *bar
+      baz
+      ====
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[1])
+    skip
+  end
+
+  def test_line_length
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      Foo
+      ------------------------------
+
+      Foo
+      =
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading2, doc.children[0])
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[1])
+  end
+
+  def test_content_indent
+    skip # TODO: implement this
+  end
+
+  def test_marker_indent
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      Foo
+          ------------------------------
+
+      Foo
+         =
+
+      Foo
+        =
+
+      Foo
+       =
+    DOC
+    refute_instance_of(::RBMark::DOM::Heading2, doc.children[0])
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[1])
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[2])
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[3])
+  end
+
+  def test_no_internal_spaces
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      Foo
+      -- - -
+
+      Foo
+      == =
+    DOC
+    refute_instance_of(::RBMark::DOM::Heading2, doc.children[0])
+    refute_instance_of(::RBMark::DOM::Heading1, doc.children[0])
+  end
+
+  def test_block_level_priority
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      ` Foo
+      ------
+      `
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading2, doc.children[0])
+    assert_instance_of(::RBMark::DOM::Paragraph, doc.children[1])
+  end
+
+  def test_paragraph_breaking_only
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      > text
+      ------
+    DOC
+    skip # TODO: implement this
+  end
+
+  def test_paragraph_breaking_only_lazy_continuation
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      > text
+      continuation line
+      ------
+    DOC
+    skip # TODO: implement this
+  end
+
+  def test_headings_back_to_back
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      heading1
+      ------
+      heading2
+      ------
+      heading3
+      ======
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading2, doc.children[0])
+    assert_instance_of(::RBMark::DOM::Heading2, doc.children[1])
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[2])
+  end
+
+  def test_no_empty_headings
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      
+      ======
+    DOC
+    refute_instance_of(::RBMark::DOM::Heading1, doc.children[0])
+  end
+
+  def test_thematic_breaks
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      ----
+      ----
+    DOC
+    refute_instance_of(::RBMark::DOM::Heading2, doc.children[0])
+    refute_instance_of(::RBMark::DOM::Heading2, doc.children[1])
+  end
+end
diff --git a/test/test_fenced_code_blocks.rb b/test/test_fenced_code_blocks.rb
new file mode 100644
index 0000000..58a038a
--- /dev/null
+++ b/test/test_fenced_code_blocks.rb
@@ -0,0 +1,102 @@
+# frozen_string_literal: true
+
+require 'minitest/autorun'
+require_relative '../lib/rbmark'
+
+# Test ATX Heading parsing compliance with CommonMark v0.31.2
+class TestATXHeadings < Minitest::Test
+  def test_simple_heading1
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      # ATX Heading level 1
+      Paragraph
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[0])
+  end
+
+  def test_simple_heading2
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      ## ATX Heading level 2
+      Paragraph
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading2, doc.children[0])
+  end
+
+  def test_simple_heading3
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      ### ATX Heading level 3
+      Paragraph
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading3, doc.children[0])
+  end
+
+  def test_simple_heading4
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      #### ATX Heading level 4
+      Paragraph
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading4, doc.children[0])
+  end
+
+  def test_simple_heading5
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      ##### ATX Heading level 5
+      Paragraph
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading5, doc.children[0])
+  end
+
+  def test_simple_heading6
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      ###### ATX Heading level 6
+      Paragraph
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading6, doc.children[0])
+  end
+
+  def test_simple_not_a_heading
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      ####### NOT a heading
+    DOC
+    assert_instance_of(::RBMark::DOM::Paragraph, doc.children[0])
+  end
+
+  def test_breaking_paragrpah
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      Paragraph 1
+      # ATX Heading level 1
+      Paragraph 2
+    DOC
+    assert_instance_of(::RBMark::DOM::Paragraph, doc.children[0])
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[1])
+    assert_instance_of(::RBMark::DOM::Paragraph, doc.children[2])
+  end
+
+  def test_heading_sans_space
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      #NOT an ATX heading
+    DOC
+    assert_instance_of(::RBMark::DOM::Paragraph, doc.children[0])
+  end
+
+  def test_heading_escaped
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      \\# Escaped ATX heading
+    DOC
+    assert_instance_of(::RBMark::DOM::Paragraph, doc.children[0])
+  end
+
+  def test_spaces
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      #### Heading level 4
+       ### Heading level 3
+        ## Heading level 2
+         # Heading level 1
+          # NOT a heading
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading4, doc.children[0])
+    assert_instance_of(::RBMark::DOM::Heading3, doc.children[1])
+    assert_instance_of(::RBMark::DOM::Heading2, doc.children[2])
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[3])
+    refute_instance_of(::RBMark::DOM::Heading1, doc.children[4])
+  end
+end
diff --git a/test/test_indent_block.rb b/test/test_indent_block.rb
new file mode 100644
index 0000000..c81e0b4
--- /dev/null
+++ b/test/test_indent_block.rb
@@ -0,0 +1,97 @@
+# frozen_string_literal: true
+
+require 'minitest/autorun'
+require_relative '../lib/rbmark'
+
+# Test Setext Heading parsing compliance with CommonMark v0.31.2
+class TestSetextHeadings < Minitest::Test
+  def test_simple_indent
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      text
+
+          indented code block
+          without space mangling
+
+          int main() {
+            printf("Hello world!\\n");
+          }
+    DOC
+    assert_instance_of(::RBMark::DOM::IndentBlock, doc.children[1])
+  end
+
+  def test_list_item_precedence
+    skip # TODO: implement this
+  end
+
+  def test_numbered_list_item_precednce
+    skip # TODO: implement this
+  end
+
+  def test_check_indent_contents
+    skip # TODO: yet again please implement this at some point thanks
+  end
+
+  def test_long_chunk
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      text
+
+          indented code block
+          without space mangling
+
+          int main() {
+            printf("Hello world!\\n");
+          }
+
+
+          there are many space changes here and blank lines that
+          should *NOT* affect the way this is parsed
+    DOC
+    assert_instance_of(::RBMark::DOM::IndentBlock, doc.children[1])
+  end
+
+  def test_does_not_interrupt_paragraph
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      Paragraph begins here
+          paragraph does the stupid wacky shit that somebody thinks is very funny
+          paragraph keeps doing that shit
+    DOC
+    assert_instance_of(::RBMark::DOM::Paragraph, doc.children[0])
+    assert_equal(1, doc.children.length)
+  end
+
+  def test_begins_at_first_sight_of_four_spaces
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      text
+
+          This is an indent block
+      This is a paragraph
+    DOC
+    assert_instance_of(::RBMark::DOM::Paragraph, doc.children[0])
+    assert_instance_of(::RBMark::DOM::IndentBlock, doc.children[1])
+    assert_instance_of(::RBMark::DOM::Paragraph, doc.children[2])
+  end
+
+  def test_interrupts_all_other_blocks
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      # Heading
+          foo
+      Heading
+      ------
+          foo
+      ----
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[0])
+    assert_instance_of(::RBMark::DOM::IndentBlock, doc.children[1])
+    assert_instance_of(::RBMark::DOM::Heading2, doc.children[2])
+    assert_instance_of(::RBMark::DOM::IndentBlock, doc.children[3])
+    assert_instance_of(::RBMark::DOM::HorizontalRule, doc.children[4])
+  end
+
+  def test_check_blank_lines_contents
+    skip # TODO: PLEASE I FUCKING BEG YOU IMPLEMENT THIS
+  end
+
+  def test_check_contents_trailing_spaces
+    skip # TODO: AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAa
+  end
+end
diff --git a/test/test_setext_headers.rb b/test/test_setext_headers.rb
new file mode 100644
index 0000000..2d1878b
--- /dev/null
+++ b/test/test_setext_headers.rb
@@ -0,0 +1,147 @@
+# frozen_string_literal: true
+
+require 'minitest/autorun'
+require_relative '../lib/rbmark'
+
+# Test Setext Heading parsing compliance with CommonMark v0.31.2
+class TestSetextHeadings < Minitest::Test
+  def test_simple_heading1
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      Foo *bar*
+      =========
+
+      Foo *bar*
+      ---------
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[0])
+    assert_instance_of(::RBMark::DOM::Heading2, doc.children[1])
+  end
+
+  def test_multiline_span
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      Foo *bar
+      baz*
+      ====
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[0])
+    assert_equal(1, doc.children.length)
+  end
+
+  def test_span_inlining
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      start
+
+        Foo *bar
+      baz
+      ====
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[1])
+    skip
+  end
+
+  def test_line_length
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      Foo
+      ------------------------------
+
+      Foo
+      =
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading2, doc.children[0])
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[1])
+  end
+
+  def test_content_indent
+    skip # TODO: implement this
+  end
+
+  def test_marker_indent
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      Foo
+          ------------------------------
+
+      Foo
+         =
+
+      Foo
+        =
+
+      Foo
+       =
+    DOC
+    refute_instance_of(::RBMark::DOM::Heading2, doc.children[0])
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[1])
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[2])
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[3])
+  end
+
+  def test_no_internal_spaces
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      Foo
+      -- - -
+
+      Foo
+      == =
+    DOC
+    refute_instance_of(::RBMark::DOM::Heading2, doc.children[0])
+    refute_instance_of(::RBMark::DOM::Heading1, doc.children[0])
+  end
+
+  def test_block_level_priority
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      ` Foo
+      ------
+      `
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading2, doc.children[0])
+    assert_instance_of(::RBMark::DOM::Paragraph, doc.children[1])
+  end
+
+  def test_paragraph_breaking_only
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      > text
+      ------
+    DOC
+    skip # TODO: implement this
+  end
+
+  def test_paragraph_breaking_only_lazy_continuation
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      > text
+      continuation line
+      ------
+    DOC
+    skip # TODO: implement this
+  end
+
+  def test_headings_back_to_back
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      heading1
+      ------
+      heading2
+      ------
+      heading3
+      ======
+    DOC
+    assert_instance_of(::RBMark::DOM::Heading2, doc.children[0])
+    assert_instance_of(::RBMark::DOM::Heading2, doc.children[1])
+    assert_instance_of(::RBMark::DOM::Heading1, doc.children[2])
+  end
+
+  def test_no_empty_headings
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      
+      ======
+    DOC
+    refute_instance_of(::RBMark::DOM::Heading1, doc.children[0])
+  end
+
+  def test_thematic_breaks
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      ----
+      ----
+    DOC
+    refute_instance_of(::RBMark::DOM::Heading2, doc.children[0])
+    refute_instance_of(::RBMark::DOM::Heading2, doc.children[1])
+  end
+end
diff --git a/test/test_thematic_breaks.rb b/test/test_thematic_breaks.rb
new file mode 100644
index 0000000..1ace973
--- /dev/null
+++ b/test/test_thematic_breaks.rb
@@ -0,0 +1,127 @@
+# frozen_string_literal: true
+
+require 'minitest/autorun'
+require_relative '../lib/rbmark'
+
+# Test thematic break parsing compliance with CommonMark v0.31.2
+class TestThematicBreaks < Minitest::Test
+  def test_simple
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      ---
+      ***
+      ___
+    DOC
+    assert_instance_of(::RBMark::DOM::HorizontalRule, doc.children[0])
+    assert_instance_of(::RBMark::DOM::HorizontalRule, doc.children[1])
+    assert_instance_of(::RBMark::DOM::HorizontalRule, doc.children[2])
+  end
+
+  def test_simple_invalid
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      +++
+    DOC
+    refute_instance_of(::RBMark::DOM::HorizontalRule, doc.children[0])
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      ===
+    DOC
+    refute_instance_of(::RBMark::DOM::HorizontalRule, doc.children[0])
+  end
+
+  def test_simple_less_characters
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      --
+
+      **
+
+      __
+    DOC
+    refute_instance_of(::RBMark::DOM::HorizontalRule, doc.children[0])
+    refute_instance_of(::RBMark::DOM::HorizontalRule, doc.children[1])
+    refute_instance_of(::RBMark::DOM::HorizontalRule, doc.children[2])
+  end
+
+  def test_indentation
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      ***
+       ***
+        ***
+         ***
+          ***
+    DOC
+    assert_instance_of(::RBMark::DOM::HorizontalRule, doc.children[0])
+    assert_instance_of(::RBMark::DOM::HorizontalRule, doc.children[1])
+    assert_instance_of(::RBMark::DOM::HorizontalRule, doc.children[2])
+    assert_instance_of(::RBMark::DOM::HorizontalRule, doc.children[3])
+    refute_instance_of(::RBMark::DOM::HorizontalRule, doc.children[4])
+  end
+
+  def test_indentation_mixed_classes
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      Foo
+
+          ***
+    DOC
+    refute_instance_of(::RBMark::DOM::HorizontalRule, doc.children.last)
+  end
+
+  def test_line_length
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      _________________________________
+    DOC
+    assert_instance_of(::RBMark::DOM::HorizontalRule, doc.children[0])
+  end
+
+  def test_mixed_spaces
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+       - - -
+
+       **  * ** * ** * **
+
+       -     -      -      -
+
+       - - - -
+    DOC
+    assert_instance_of(::RBMark::DOM::HorizontalRule, doc.children[0])
+    assert_instance_of(::RBMark::DOM::HorizontalRule, doc.children[1])
+    assert_instance_of(::RBMark::DOM::HorizontalRule, doc.children[2])
+    assert_instance_of(::RBMark::DOM::HorizontalRule, doc.children[3])
+  end
+
+  def test_mixed_characters
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      _ _ _ _ a
+
+      a------
+
+      ---a---
+    DOC
+    refute_instance_of(::RBMark::DOM::HorizontalRule, doc.children[0])
+    refute_instance_of(::RBMark::DOM::HorizontalRule, doc.children[2])
+    refute_instance_of(::RBMark::DOM::HorizontalRule, doc.children[3])
+  end
+
+  def test_mixed_markets
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+       *-*
+    DOC
+    refute_instance_of(::RBMark::DOM::HorizontalRule, doc.children[0])
+  end
+
+  def test_interrupt_list
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      - foo
+      ***
+      - bar
+    DOC
+    assert_instance_of(::RBMark::DOM::HorizontalRule, doc.children[1])
+  end
+
+  def test_interrupt_paragraph
+    doc = ::RBMark::DOM::Document.parse(<<~DOC)
+      foo
+      ***
+      bar
+    DOC
+    assert_instance_of(::RBMark::DOM::HorizontalRule, doc.children[1])
+  end
+end