Sitecore PageExtenders: non greedy approach

   There is great Sitecore feature: Page Extenders. It allows you to insert any HTML code to your pages. However inaccurate usage of it can harm your site.
   

    Once I installed Federated Experience Manager on Sitecore 7.2 I was unable to get it worked. For some reasons JavaScript on its pages failed. After deeper investigation I found that on any FxM request to server I got incorrect JSON. It was well formed, but at the end string

<input name="SC_ANALYTICS_PAGE" type="hidden" id="SC_ANALYTICS_PAGE" value="ecbb31a2-4c43-494d-88a1-811994213a89" /> 

was added. I figured out that this string was added by SBOS Accelerator module that was installed few days before. Reason of adding this string was greedy PageExеnder. It added this string everywhere, except few sites(shell, modules_shell). Such behavior also break some admin pages, e.g.: ShowConfig.aspx.

   After fixing this problem I can make conclusion: that in general it is much more better to specify where PageExtender should insert controls rather than specify where it should not insert controls. Even if you add a lot of exceptions, you could not cover by your exceptions everything that could appear in custom solutions.