Shallow markup
I should note a hefty error in the last few posts. I loftily concluded that shallow markup languages were beneficial, without actually mentioning any real-world examples. The best place to start at would be looking at Markdown, which unfortunately covers far too little of the semantic range of HTML5 to be useful for authoring, but re-workings like ReMarkable show that the syntax can be extended far enough (though even there still more tweaks are needed).
I am not worried about storing large volumes of text in a custom format, as long as only a small amount of code is needed to transform it to XML.