when an article edited in html starts with <section> tag, content is not rendered

[volapuk]

I use to edit my articles in html, the article is divided in sections and subsections using <section> html5 tag, id an article starts with that tag content is not rendered in web, as a workarround I have to put an space char (&nbsp;) and then the content is correctly rendered.
This happens with all versions of wordpress.

[noisysocks]

The code editor is only designed for editing basic post markup (<p>, <strong>, <a>, etc.) in a way that's conducive to writing a post. That's why, for example, wpautop replaces double new lines with paragraph tags by default.

You might find that disabling wp_kses and wpautop is what would best suit your needs.