--- a/testing/marionette/element.js
+++ b/testing/marionette/element.js
@@ -6,16 +6,17 @@
 /* global XPCNativeWrapper */
 
 const {classes: Cc, interfaces: Ci, utils: Cu} = Components;
 
 Cu.import("chrome://marionette/content/assert.js");
 Cu.import("chrome://marionette/content/atom.js");
 const {
   InvalidArgumentError,
+  InvalidElementStateError,
   InvalidSelectorError,
   NoSuchElementError,
   StaleElementReferenceError,
 } = Cu.import("chrome://marionette/content/error.js", {});
 const {pprint} = Cu.import("chrome://marionette/content/format.js", {});
 const {PollPromise} = Cu.import("chrome://marionette/content/sync.js", {});
 
 this.EXPORTED_SYMBOLS = [
@@ -936,16 +937,43 @@ element.isEditable = function(el) {
   if (element.isReadOnly(el) || element.isDisabled(el)) {
     return false;
   }
 
   return element.isMutableFormControl(el) || element.isEditingHost(el);
 };
 
 /**
+ * Tests that <var>el</var> satisfies all its form control constraints.
+ *
+ * An element is considered <em>not</em> to satisfy its constraints
+ * if it suffers from being missing, its input has a value that is
+ * not the correct syntax (email, URL), does not satisfy the
+ * <code>pattern</code> attribute, is too long (<code>maxlength</code>)
+ * or too short (<code>minlength</code>), overflows or underflows,
+ * does not fit the rules of the <code>step</code> attribute,
+ * or otherwise has incomplete input according to Gecko.
+ *
+ * @param {Element} el
+ *     Mutable form control element.
+ *
+ * @return {boolean}
+ *     True if it satisfies all its constraints.
+ *
+ * @throws {InvalidElementStateError}
+ *     If <var>el</var> is not a mutable form control element.
+ */
+element.satisfiesConstraints = function(el) {
+  if (!element.isMutableFormControl(el)) {
+    throw new InvalidElementStateError(pprint`Not an editable form control: ${el}`);
+  }
+  return el.validity.valid;
+};
+
+/**
  * This function generates a pair of coordinates relative to the viewport
  * given a target element and coordinates relative to that element's
  * top-left corner.
  *
  * @param {Node} node
  *     Target node.
  * @param {number=} xOffset
  *     Horizontal offset relative to target's top-left corner.