The command \url is a form of verbatim command that allows linebreaks at
certain characters or combinations of characters, accepts reconfiguration, and
can usually be used in the argument to another command. (The \urldef command
provides robust commands that serve in cases when \url doesn't work in an
argument.) The command is intended for email addresses, hypertext links,
directories/paths, etc., which normally have no spaces, so by default the
package ignores spaces in its argument. However, a package option "allows
spaces", which is useful for operating systems where spaces are a common part
of file names.
