I'm trying to grab a string inside a web page and am having issues with varying cases on the surrounding text. I think I want a regex function (preg_grep?), but I'm not sure which one or how to write it.

Here is an example of the strings I'm trying to parse:
Part Number:</B> 1234atoz<BR><B>

Part Number:</b> 1234atoz<br><b>
I'm trying to grab just the "1234atoz" portion which can be any combination and length of alphanumerics. I want to maintain the case of the portion I'm grabbing, but ignore the case of the other parts. The html varies from upper case to lower case which is making my life difficult.

Thanks for your help!