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 some <a href="/?a&b">html</a> code 
 ^$b^(2+2^) 
 \^\(\.\*\?\)\$ 
 some <?dirty?> code 

 some &lt;a href=&quot;/?a&amp;b&quot;&gt;html&lt;/a&gt; code 
 ^$b^(2+2^) 
 \^\(\.\*\?\)\$ 
 some &lt;?dirty?&gt; code 

 some &lt;a href=&quot;/?a&amp;b&quot;&gt;html&lt;/a&gt; code 
 ^$b^(2+2^) 
 \^\(\.\*\?\)\$ 
 some <\?dirty\?> code 

 some &lt;a href=&quot;/?a&amp;b&quot;&gt;html&lt;/a&gt; code 
 ^$b^(2+2^) 
 \^\(\.\*\?\)\$ 
 some <?dirty?> code