This is something I've been wondering for a while now. I'll occasionally come across an RSS feed that is broken, and blown to pieces all because line 23 say "Sanford & Sons." The most confusing thing is the fact that if you convert the & into &, all is well, even though your alternative still contains the problem-char!
Please somebody explain this confusing mystery to me.
When a 'raw' & is seen, the interpreter is looking for one of the valid escaped & sequences (such as '&' ). When a valid sequence is found found it throws an error. That's all there is to it.
This depends highly on the RSS client, but most likely it's attempting to XML-decode the contents (in your example "Sanford & Sons"). When that happens, & indicates an escaped character. If you don't use & as it decodes, it will try to use the next few characters to complete the escape sequence. Odds are highly likely that it will fail.
Because RSS is XML, and XML demands certain characters be escaped, such as the ampersand.
Because & signifies the start of an xml entity. The parser is expecting something else there.
You could argue that it should be smart enough to know that the ampersand in "Sanford & Sons" is just an ampersand. But what about when you really want to show ampersand with text? Is "&pc; some custom (also invalid) entity, or should it interpret that as an ampersand also? What about "&"?
Not sure if this helps but when I needed to solve this problem I used the numeric entity ref for an ampersand which is & Running this through the w3c validator passed so I guess it's ok to use this.
Cheers