References in PHP are a means to access the same variable content
by different names. They are not like C pointers; instead, they are
symbol table aliases. Note that in PHP, variable name and variable
content are different, so the same content can have different names.
The most close analogy is with Unix filenames and files -
variable names are directory entries, while variable contents is
the file itself. References can be thought of as hardlinking in
Unix filesystem.
