codeguy/php-the-right-way — pull request #334 by weakish (2013-12-07 12:08:00+00:00)
Title: higher order function

Higher order functions use functions as input and/or output.

> Functions can be passed as arguments to other functions (a feature called higher-order functions) and a function can return other functions.

This may cause confusion that only functions using functions as input are higher-order functions.

Thus I tweak the text a bit.