I am faced with the following issue for which I am unable to think of a good solution inspite of using regular expressions. Please help with suggestions

I have a HTML file, which I would to highlight certain parts of the content (sentences) with the 

```
"<span style="background-color:#FFFF00">...</span>" 

```

code, so that those parts are highlighted. Seems straighforward, but, the issue is that the HTML file I have contains useful information with all kinds of junk in between. Lets say the string I am interested in highlighting in my string is A= "I am pretty screwed up with this HTML"

the original HTML code looks like :

```
......<span class="_ _3"> </span>I<span class="_ _3"> </span> <span class="fc3">am</span> pretty<span  class="_ _3"> </span>screw<span class="_ _3">ed</span> <span class="_ _3"> </span>up</div> <div class="t m0 x19 hb y5f ff4 fs7 fc2 sc0 ls0 ws0">with this<span class="_ _3"> </span><span class="ff7">HT<span class="_ _8"></span></span>ML</div>.....

```

I would like to use regular expressions to find the original string A and add the highlight element around it. So the final output should be

```
......<span class="_ _3"> </span><span style="background-color:#FFFF00">I</span><span class="_ _3"> </span> <span class="fc3"><span style="background-color:#FFFF00">am</span></span> <span style="background-color:#FFFF00">pretty</span><span  class="_ _3"> </span><span style="background-color:#FFFF00">screw</span><span class="_ _3"><span style="background-color:#FFFF00">ed</span></span> <span class="_ _3"> </span><span style="background-color:#FFFF00">up</span></div> <div class="t m0 x19 hb y5f ff4 fs7 fc2 sc0 ls0 ws0"><span style="background-color:#FFFF00">with this</span><span class="_ _3"> </span><span class="ff7"><span style="background-color:#FFFF00">HT</span><span class="_ _8"></span></span><span style="background-color:#FFFF00">ML</span></div>.....

```