People who want to produce a syndication feed in a consistently correct manner will find that they will need to master not only the syndication format, but also HTML, and XML. It is all too easy to underestimate the total learning curve involved. I continue to be surprised at the subtle interactions that continue to trip up even the most knowledgeable and careful.
My experience is that people learn best by examples. Simple examples. This works best when the examples have been carefully chosen to illustrate a specific principle.
In this series of examples, I have chosen a lone ampersand, preferably with a font-weight of bold. These examples employed a variety of approaches synthesized based on what I have seen out in the wild. Some of the examples presume that the producer strips out all markup.
For the moment, I have also chosen the title element, but I could have chosen description, summary, or even content:encoded. Can you imagine a title with an ampersand character? I knew that you could.
Note: while the number of these tests may surprise some, they are by no means exhaustive. In HTML, font-weight can also be defined using style attributes or with font tags. In XML, arbitrary groupings of characters may be grouped as CDATA.
My ultimate goal is to produce a comprehensive guide for toolbuilders that produce Atom feeds. If you know of a tool that produces a variation that is not included in this list, please let me know.