How to Solve Open XML Developer Problems

A question recently came up in one of the forums: How do you insert a horizontal line below a paragraph? I decided to use this question as the focus of a screen-cast that shows the general approach that I use to solve Open XML developer problems. The general gist of the approach is that I create two documents, one without the feature of interest, and one with. I then use the Open XML SDK productivity tool to compare the two and find out the differences. I then use the Open XML Package Editor Power Tool for Visual Studio 2010 to examine the markup, and I use the PDF form of the ECMA 376 Second Edition Part 1 to research the markup.