Handling iFrame

http://toolsqa.com/selenium-webdriver/handling-iframes-using-selenium-webdriver/  

https://www.seleniumeasy.com/selenium-tutorials/how-to-work-with-iframes-in-selenium-webdriver 

http://www.guru99.com/handling-iframes-selenium.html

https://github.com/facebook/php-webdriver/wiki/Alert,-Window-Tab,-frame-iframe-and-active-element 

http://www.assertselenium.com/webdriver/handling-iframes-using-webdriver/