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Hey there! The 'Document Text' does refer to the text on the page - I'm afraid though it is possible that the On-Page Grader isn't counting keywords used on the page correctly. We have seen this before, and the team has made the decision that they're not going to be pursuing fixes for the On-Page Grader tool at this time. The same functionality is available through the Page Optimization section of your campaigns, and in the Page Optimization tool from the MozBar, and those tools are far more reliable than the On-Page Grader. We'd recommend using the these instead for all your Page Optimization needs going forward. If you're still running into the same problem using the Page Optimization tool, please do pop a message over to help@moz.com with an example of a keyword/URL combination, and we'll be more than happy to investigate.