The phptags utility makes a tags file from the
specified PHP sources. A tags file gives the
locations of specified objects in a group of
files. Each line of the tags file contains the
object name, the file in which it is defined, and
a search pattern for the object definition,
separated by whitespace. Using the tags file, many
editors (ex(1), vim(1), emacs(1), etc.) can
quickly locate these object definitions.