Methods and systems are configured for tracking content represented in a resource. A modified version of structure data of a resource that includes at least one element is received. Each element represents content of the resource in the structure data. Each element includes a portion of the structure data that defines the content. Data specifying a target element of the structure data is received. A plurality of locators for the target element are obtained. A locator of the plurality is derived as a function of a frequency that one or both of attributes and classes of the target element appear in the structure data and includes a subset of the attributes and the classes, the subset uniquely identifying the target element. The plurality of locators including the locator are applied to a modified version of the structure data to extract a modified version of the target element.