lass='tstring_end'>&#39;</span></span>
  <span class='kw'>when</span> <span class='symbol'>:png</span> <span class='kw'>then</span> <span class='tstring'><span class='tstring_beg'>&#39;</span><span class='tstring_content'>image/png</span><span class='tstring_end'>&#39;</span></span>
  <span class='kw'>else</span> <span class='tstring'><span class='tstring_beg'>&quot;</span><span class='tstring_content'>image/</span><span class='embexpr_beg'>#{</span><span class='ivar'>@format</span><span class='embexpr_end'