Lib for well-known functions

This reveals a lexer bug that needs addressing.

src/ol/expression/expression.js

@@ -1,6 +1,10 @@
 goog.provide('ol.expression');
 
+goog.require('ol.Extent');
+goog.require('ol.Feature');
 goog.require('ol.expression.Parser');
+goog.require('ol.extent');
+goog.require('ol.geom.GeometryType');
 
 
 /**
@@ -13,3 +17,49 @@ ol.expression.parse = function(source) {
   var parser = new ol.expression.Parser();
   return parser.parse(source);
 };
+
+
+/**
+ * Library of well-known functions.  These are available to expressions parsed
+ * with `ol.expression.parse`.
+ *
+ * @type {Object}
+ */
+ol.expression.lib = {
+
+  /**
+   * Determine if a feature's extent intersects the provided extent.
+   * @param {number} minX Minimum x-coordinate value.
+   * @param {number} maxX Maximum x-coordinate value.
+   * @param {number} minY Minimum y-coordinate value.
+   * @param {number} maxY Maximum y-coordinate value.
+   * @return {boolean} The provided extent intersects the feature's extent.
+   * @this {ol.Feature}
+   */
+  'extent': function(minX, maxX, minY, maxY) {
+    var intersects = false;
+    var geometry = this.getGeometry();
+    if (geometry) {
+      intersects = ol.extent.intersects(geometry.getBounds(),
+          [minX, maxX, minY, maxY]);
+    }
+    return intersects;
+  },
+
+
+  /**
+   * Determine if a feature's default geometry is of the given type.
+   * @param {ol.geom.GeometryType} type Geometry type.
+   * @return {boolean} The feature's default geometry is of the given type.
+   * @this {ol.Feature}
+   */
+  'geometryType': function(type) {
+    var same = false;
+    var geometry = this.getGeometry();
+    if (geometry) {
+      same = geometry.getType() === type;
+    }
+    return same;
+  }
+
+};