Restricting the number of times a rendering can be added to a placeholder

This is another one of those tasks that shouldn't really be necessary to do. Every time a client says "We don't want two of these components added to this placeholder" my answer is always "So don't add two." It's a people problem that companies want solved with technology. This solution is geared more toward the use of the Experience Editor and it is going to stop a rendering appearing in the "Select a rendering" dialog if it already exists in that placeholder the maximum number of times.

Post-Processing html after it has been generated in Sitecore

Sometimes we might want to do an operation on the entire html generated for a page, such as move elements around, do some text replacements or regex-based url amendments.  The MVC framework has various features like action filters, result filters and so on, but we can't really use these with Sitecore the same way we would a native MVC site.  In traditional MVC your page is the result of a single action, but in Sitecore it is lots of actions stitched together so there is a little more work to do, so let's get started.

Sitecore pipelines in high volume sites

Introduction

If you use class-level variables in your Sitecore pipelines you might discover inconsistent and unwanted behaviour.