[js] add documentation for js.lib.RegExp (closes #9300)

std/js/lib/RegExp.hx

@@ -29,22 +29,78 @@ import haxe.DynamicAccess;
 
 	For cross-platform regular expressions, use Haxe `EReg` class or
 	[regexp literals](https://haxe.org/manual/std-regex.html).
+
+	@see <https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp>
 **/
 @:native("RegExp")
 extern class RegExp {
+	/**
+		Indicates whether or not the "g" flag is used with the regular expression.
+	**/
 	var global(default, null):Bool;
+
+	/**
+		Indicates whether or not the "i" flag is used with the regular expression.
+	**/
 	var ignoreCase(default, null):Bool;
+
+	/**
+		Indicates whether or not the "m" flag is used with the regular expression.
+	**/
 	var multiline(default, null):Bool;
+
+	/**
+		The source text of the regexp object, it doesn't contain the two forward slashes on both sides and any flags.
+	**/
 	var source(default, null):String;
+
+	/**
+		The index at which to start the next match.
+	**/
 	var lastIndex:Int;
+
+	/**
+		Create a regular expression object for matching text with a pattern.
+	**/
 	function new(pattern:String, ?flags:String);
+
+	/**
+		Execute a search for a match in a specified string.
+		Returns a result array, or null.
+	**/
 	function exec(str:String):Null<RegExpMatch>;
+
+	/**
+		Execute a search for a match between a regular expression and a specified string.
+		Returns true or false.
+	**/
 	function test(str:String):Bool;
+
+	/**
+		Return a string representing the regular expression.
+	**/
 	function toString():String;
 }
 
+/**
+	A return value of the `RegExp.exec` method.
+**/
 extern class RegExpMatch extends Array<String> {
+	/**
+		The index of the search at which the result was found.
+	**/
 	var index:Int;
+
+	/**
+		A copy of the search string.
+	**/
 	var input:String;
-	var groups:DynamicAccess<String>;
+
+	/**
+		Named capturing groups or undefined if no named capturing groups were defined.
+		See [Groups and Ranges](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions/Groups_and_Ranges) for more information.
+
+		Note: Not all browsers support this feature; refer to the [compatibility table](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions#Browser_compatibility).
+	**/
+	var groups:Null<DynamicAccess<String>>;
 }