What does “proxy to” mean?

Question

I keep coming across the word "proxy" used as a verb in tutorials, etc. Usually something will "proxy to" something else. What does this mean?

Having spent some time googling for what it means in a programming context, I mostly found "proxy server" or some other noun use. I understand the word proxy generally means "a stand in," so "proxy to" must mean "to stand in for." Right? But I'm still confused, because it doesn't seem to be used like that.

An example (from a PHP ZF tutorial): "__get(), __set(), __isset(), and __call(): All of these methods simply proxy to the row instance stored in $_row. This provides an easy way to composite Zend_Db_Table_Row with our Model Resource Item." from Keith Pope, Zend Framework 1.8 Web Application Development, 2009.

What does the author mean by "proxy to" in this context?