1. A method for determining whether a first region within a web page is in view, comprising: providing, within the web page, a first test feature having a behavioral characteristic, wherein a measured value of the behavioral characteristic varies in response to whether the first test feature is in view or not in view within a viewable area of the web page at a time of measurement; monitoring, using code restricted from accessing a position of the first region within the web page, a variation of the behavioral characteristic of the first test feature as the first test feature is moved between the first region and a second region known to be out of the viewable area; providing, within the web page, a second test feature having the behavioral characteristic and maintained within the first region; measuring, using the code, a value of the behavioral characteristic of the second test feature; and determining whether the first region is within the viewable area of the web page using the variation of the behavioral characteristic of the first test feature and the measured value of the behavioral characteristic of the second test feature.