Merge pull request expressjs#51 from etiktin/master

Update README.md

README.md

@@ -164,15 +164,20 @@ app.listen(80, function(){
 
 ## Configuration Options
 
-* `origin`: Configures the **Access-Control-Allow-Origin** CORS header. Expects a string (ex: "http://example.com"). Set to `true` to reflect the [request origin](http://tools.ietf.org/html/draft-abarth-origin-09), as defined by `req.header('Origin')`. Set to `false` to disable CORS. Can also be set to a function, which takes the request origin as the first parameter and a callback (which expects the signature `err [object], allow [bool]`) as the second. Finally, it can also be a regular expression (`/example\.com$/`) or an array of regular expressions and/or strings to match against.
+* `origin`: Configures the **Access-Control-Allow-Origin** CORS header. Possible values:
+ - `Boolean` - set `origin` to `true` to reflect the [request origin](http://tools.ietf.org/html/draft-abarth-origin-09), as defined by `req.header('Origin')`, or set it to `false` to disable CORS. 
+ - `String` - set `origin` to a specific origin. For example if you set it to `"http://example.com"` only requests from "http://example.com" will be allowed.
+ - `RegExp` - set `origin` to a regular expression pattern which will be used to test the request origin. If it's a match, the request origin will be reflected. For example the pattern `/example\.com$/` will reflect any request that is coming from an origin ending with "example.com".
+ - `Array` - set `origin` to an array of valid origins. Each origin can be a `String` or a `RegExp`. For example `["http://example1.com", /\.example2\.com$/]` will accept any request from "http://example1.com" or from a subdomain of "example2.com".
+ - `Function` - set `origin` to a function implementing some custom logic. The function takes the request origin as the first parameter and a callback (which expects the signature `err [object], allow [bool]`) as the second.
 * `methods`: Configures the **Access-Control-Allow-Methods** CORS header. Expects a comma-delimited string (ex: 'GET,PUT,POST') or an array (ex: `['GET', 'PUT', 'POST']`).
 * `allowedHeaders`: Configures the **Access-Control-Allow-Headers** CORS header. Expects a comma-delimited string (ex: 'Content-Type,Authorization') or an array (ex: `['Content-Type', 'Authorization']`). If not specified, defaults to reflecting the headers specified in the request's **Access-Control-Request-Headers** header.
 * `exposedHeaders`: Configures the **Access-Control-Expose-Headers** CORS header. Expects a comma-delimited string (ex: 'Content-Range,X-Content-Range') or an array (ex: `['Content-Range', 'X-Content-Range']`). If not specified, no custom headers are exposed.
 * `credentials`: Configures the **Access-Control-Allow-Credentials** CORS header. Set to `true` to pass the header, otherwise it is omitted.
 * `maxAge`: Configures the **Access-Control-Allow-Max-Age** CORS header. Set to an integer to pass the header, otherwise it is omitted.
 * `preflightContinue`: Pass the CORS preflight response to the next handler.
 
-For details on the effect of each CORS header, [read this article on HTML5 Rocks](http://www.html5rocks.com/en/tutorials/cors/).
+For details on the effect of each CORS header, read [this](http://www.html5rocks.com/en/tutorials/cors/) article on HTML5 Rocks.
 
 ## Demo