Embed PHP in HTML using “:” operator

[SockSwece]

In an effort to produce cleaner PHP files, I want to echo less HTML and embed more PHP. I've stumbled upon constructs like the following:\[code\]<?phpforeach($allOGroups as $ogroup):if($lastGroup != $ogroup['group']):if($lastGroup !== null):?></optgroup><?phpendif;?>\[/code\]I've googled for a while now but can't seem to find a tutorial on how to use this mysterious ":" operator. Can anyone point me in the right direction?Thanks,MrB