Add a "fields" filter operator

core/modules/filters/fields.js

@@ -0,0 +1,42 @@
+/*\
+title: $:/core/modules/filters/fields.js
+type: application/javascript
+module-type: filteroperator
+
+Filter operator for returning the names of the fields on the selected tiddlers
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+/*
+Export our filter function
+*/
+exports.fields = function(source,operator,options) {
+	var self = this,
+		results = [];
+	// Function to check an individual title
+	function checkTiddler(title) {
+		// Return the fields on the specified tiddler
+		var tiddler = options.wiki.getTiddler(title);
+		for(var fieldName in tiddler.fields) {
+			$tw.utils.pushTop(results,fieldName);
+		}
+	}
+	// Iterate through the source tiddlers
+	if($tw.utils.isArray(source)) {
+		$tw.utils.each(source,function(title) {
+			checkTiddler(title);
+		});
+	} else {
+		$tw.utils.each(source,function(element,title) {
+			checkTiddler(title);
+		});
+	}
+	return results;
+};
+
+})();