Implemented usingbygroup action, so code-in-markdown works

src/actions.cr

@@ -16,13 +16,16 @@ module Tartrazine
     Push
     Token
     Using
+    Usingbygroup
     Usingself
   end
 
   struct Action
     property actions : Array(Action) = [] of Action
 
+    @content_index : Int32 = 0
     @depth : Int32 = 0
+    @lexer_index : Int32 = 0
     @lexer_name : String = ""
     @states : Array(String) = [] of String
     @states_to_push : Array(String) = [] of String
@@ -62,6 +65,9 @@ module Tartrazine
         @states = xml.attributes.select { |attrib|
           attrib.name == "state"
         }.map &.content
+      when ActionType::Usingbygroup
+        @lexer_index = xml["lexer"].to_i
+        @content_index = xml["content"].to_i
       end
     end
 
@@ -134,6 +140,12 @@ module Tartrazine
         tokenizer.lexer.states[new_state.name] = new_state
         tokenizer.state_stack << new_state.name
         [] of Token
+      when ActionType::Usingbygroup
+        # Shunt to content-specified lexer
+        return [] of Token if match.empty?
+        Tartrazine.lexer(String.new(match[@lexer_index].value)).tokenizer(
+          String.new(match[@content_index].value),
+          secondary: true).to_a
       else
         raise Exception.new("Unknown action type: #{@type}")
       end

src/lexer.cr

@@ -12,24 +12,24 @@ module Tartrazine
   def self.lexer(name : String? = nil, filename : String? = nil) : BaseLexer
     return lexer_by_name(name) if name && name != "autodetect"
     return lexer_by_filename(filename) if filename
-  
+
     Lexer.from_xml(LexerFiles.get("/#{LEXERS_BY_NAME["plaintext"]}.xml").gets_to_end)
   end
-  
+
   private def self.lexer_by_name(name : String) : BaseLexer
     lexer_file_name = LEXERS_BY_NAME.fetch(name.downcase, nil)
     return create_delegating_lexer(name) if lexer_file_name.nil? && name.includes? "+"
     raise Exception.new("Unknown lexer: #{name}") if lexer_file_name.nil?
-  
+
     Lexer.from_xml(LexerFiles.get("/#{lexer_file_name}.xml").gets_to_end)
   end
-  
+
   private def self.lexer_by_filename(filename : String) : BaseLexer
     candidates = Set(String).new
     LEXERS_BY_FILENAME.each do |k, v|
       candidates += v.to_set if File.match?(k, File.basename(filename))
     end
-  
+
     case candidates.size
     when 0
       lexer_file_name = LEXERS_BY_NAME["plaintext"]
@@ -38,16 +38,17 @@ module Tartrazine
     else
       raise Exception.new("Multiple lexers match the filename: #{candidates.to_a.join(", ")}")
     end
-  
+
     Lexer.from_xml(LexerFiles.get("/#{lexer_file_name}.xml").gets_to_end)
   end
-  
+
   private def self.create_delegating_lexer(name : String) : BaseLexer
     language, root = name.split("+", 2)
     language_lexer = lexer(language)
     root_lexer = lexer(root)
     DelegatingLexer.new(language_lexer, root_lexer)
   end
+
   # Return a list of all lexers
   def self.lexers : Array(String)
     LEXERS_BY_NAME.keys.sort!