Useability is not good

Well, HTML and pretty much any concrete XML format I have ever had the displeasure of dealing with. The basic design of the entity system is just deeply flawed when compared to much simpler escaping mechanism in other text formats. I'd much rather deal with five levels of backslash escaping in a template that generates shell code that uses regular expression parameters to modify some other stuff with backslash escaping than with XML and that is not because nested backslash escaping is fun to deal with (especially when each level has slightly different things that need backslash escaping).