function verifyUserName(string)
  {
   /* Custom-built function that checks for a valid user name (string) format. If the string
    * is invalid, the function returns false. Otherwise, the function returns true.
    *
    * Regular expressions are delimited by forward slashes (/).
    *        . matches any singular character.
    *        ? matches one or none of the preceding character.
    *        + matches at least one of the preceding character.
    *        * matches none or all of the preceding character.
    *        ^ matches the absolute beginning of the string.
    *        $ matches the absolute end of the string.
    *       \d matches any decimal digit.
    *       \D matches any character that is not a decimal digit.
    *       \s matches any whitespace character. 
    *       \S matches any character that is not a whitespace character.
    *      \w+ matches a whole word.
    *       \w matches a "word" character (alphanumerics and the "_" character).
    *       \W matches any "non-word" character. 
    *      x|y matches one or the other of x or y.
    *   [0..9] matches ONE number, ranging from 0 to 9.
    * [A-Za-z] matches any letter, uppercase or lowercase.
    */

   if (string.search(/^\w+( \w+)?$/) != -1)
      {return true; }
   else
      {return false;}
  }