There is no "underlying html", the data is stored as dhtml and the html the browser gets is mostly generated at run-time.
I'd have a look at https://marketplace.atlassian.com/plugins/com.atlassian.confluence.plugins.editor.confluence-source-editor as I think it's the closest you'll get.
If you are in Edit mode, have a look in the top right corner of the editor. There should be a button with this on it: <>
If you click on that you can edit the HTML for that page. This button will only appear if the page has already been saved once.
Also, we're running 4.3.7 and have it installed locally.
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