}
config(
msg?: string | ConfigCallback,
parseFn?: ConfigCallback
): YargsInstance {
argsert(
'[object|string] [string|function] [function]',
[key, msg, parseFn],
arguments.length
);
// allow a config object to be provided directly.
if (typeof key === 'object' && !Array.isArray(key)) {
key = applyExtends(
key,