code: def blockdiag_parser(preprocessor, tag, markup):
      
      m = DOT_BLOCK_RE.search(markup)
      if m:
          # Get diagram type and code
          diagram = m.group('diagram').strip()
          code = markup
  
          # Run command
          output = diag(code, diagram)
  
          if output:
              # Return Base64 encoded image
              return '<span class="blockdiag" style="align: center;"><img src="data:image/png;base64,%s"></span>' % base64.b64encode(output)
      else:
          raise ValueError('Error processing input. '
                           'Expected syntax: {0}'.format(SYNTAX))
docs: Blockdiag parser