How to use regex for multiple line pattern in shell script

How to use regex for multiple line pattern in shell script

I want to write a bash script that finds a pattern in a html-file which is
going over multiple lines.
File for regex:
<td class="content">
some content
</td>
<td class="time">
13.05.2013 17:51
</td>
<td class="author">
A Name
</td>
Now I want to find the content of <td>-tag with the class="time".
So in principle the following regex:
<td class="time">(\d{2}\.\d{2}\.\d{4}\s+\d{2}:\d{2})</td>
grep seems not to be the command I can use, because...
It only returns the complete line or the complete result using -o and not
only the result inside the round brackets (...).
It looks only in one line for a pattern
So how is it possible that I will get only a string with 13.05.2013 17:51?