support for variables in title

lib/jekyll/tags/rtitle.rb

@@ -7,10 +7,10 @@ module Jekyll
         end
 
         def initialize(tag_name, block_options, liquid_options)
+            @markup = block_options
             super
 
             args = split_params(block_options)
-            @title = args[0]
 
             # Optional - setting your own ID
             if args.length > 1
@@ -19,23 +19,47 @@ module Jekyll
                 @block_id_html = ""
             end
         end
-  
+
+        # similar solution proposed here: https://stackoverflow.com/a/45393697
+        def get_value(context, expr)
+            args = split_params(expr)
+
+            # title in quotes, either double or single
+            if (expr[0]=='"' and expr[-1]=='"') or (expr[0]=="'" and expr[-1]=="'")
+                return expr[1..-2]
+
+            # expression contains a dot and is not longer than 20 characters
+            elsif expr.include? "." and args[0].length < 20
+                vars = expr.split('.')
+                result = context
+                vars.each do |variable|
+                    result = result[variable] if result
+                end
+                return result
+
+            # title is given as a sequence of words
+            else
+                return args[0]
+            end
+        end
+
         def render(context)
             site = context.registers[:site]
             converter = site.find_converter_instance(::Jekyll::Converters::Markdown)
             content = converter.convert(super)
+            title = get_value(context, @markup.strip)
             output = <<~EOS
 <div class="rtitle"#{@block_id_html}>
-<h2>#{@title}</h2>
+<h2>#{title}</h2>
 <hr>
     #{content}
 </div>
     EOS
-        
+
             output
         end
       end
     end
   end
-  
+
 Liquid::Template.register_tag('rtitle', Jekyll::Tags::RtitleTag)