+/**
+ * check if given string is a valid command line for any writer
+ *
+ * \param \wa string of the form writer_name:options
+ * \param writer_num contains the number of the writer upon success
+ *
+ * This function checks whether \a wa starts with the name of a supported
+ * paraslash writer, optinally followed by a colon and any options for that
+ * writer. If a valid writer name was found and further are present, the
+ * remaining part of \a wa is passed to that writer's config parser.
+ *
+ * \return On success, a pointer to the gengetopt args info struct is returned
+ * and \a writer_num contains the number of the writer. Otherwise this function
+ * returns \p NULL.
+ */