[babesh]

It's not a written down list. The way it works is that when you are considered for a company, someone there might reach out to people they know at your former or current employer and get the inside info on you. Those people are usually higher up the hierarchy than you. So if they have some grudge they hold against you, then you won't get hired irrespective of how you did in the interview and you will never know the real reason.

This is the hidden power structure that crosses companies. And this power structure holds and maintains all sorts of biases: alumni, ethnicity, religion, gender, socioeconomic, etc... It works the other way too in terms of some people getting hired who otherwise wouldn't.

In fact, that person holds the relationship with the other person in higher regard than you and will in fact report to the other person that you have been interviewing at another company. Applies to recruiters, managers, HR, you name it.