+/**
+ * Create dropdown HTML content of users.
+ *
+ * The content can either be displayed, which it is by default or retrieved by
+ * setting the 'echo' argument. The 'include' and 'exclude' arguments do not
+ * need to be used; all users will be displayed in that case. Only one can be
+ * used, either 'include' or 'exclude', but not both.
+ *
+ * The available arguments are as follows:
+ * <ol>
+ * <li>show_option_all - Text to show all and whether HTML option exists.</li>
+ * <li>show_option_none - Text for show none and whether HTML option exists.
+ * </li>
+ * <li>orderby - SQL order by clause for what order the users appear. Default is
+ * 'display_name'.</li>
+ * <li>order - Default is 'ASC'. Can also be 'DESC'.</li>
+ * <li>include - User IDs to include.</li>
+ * <li>exclude - User IDs to exclude.</li>
+ * <li>multi - Default is 'false'. Whether to skip the ID attribute on the 'select' element.</li>
+ * <li>show - Default is 'display_name'. User table column to display. If the selected item is empty then the user_login will be displayed in parentesis</li>
+ * <li>echo - Default is '1'. Whether to display or retrieve content.</li>
+ * <li>selected - Which User ID is selected.</li>
+ * <li>name - Default is 'user'. Name attribute of select element.</li>
+ * <li>class - Class attribute of select element.</li>
+ * </ol>
+ *
+ * @since 2.3.0
+ * @uses $wpdb WordPress database object for queries
+ *
+ * @param string|array $args Optional. Override defaults.
+ * @return string|null Null on display. String of HTML content on retrieve.
+ */