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.
