Google released new passback tags for GPT (DFP) a while back. While these tags appear to work, they don’t comply with W3C standards. E.g
googletag.pubads().definePassback('/7146/adunit', [300, 250]).display();
It seems you can have either src or text between the tags, not both. It generates this error:
line 533 column 9 – Error: The text content of element script was not in the required format: Expected space, tab, newline, or slash but found g instead.
I’m unsure of a solution at the moment. I have raised this issue with our account manager, but I don’t expect any fixes anytime soon.