Sometime it is required to add some html5 tags in content block. If you try to do that, the TinyMCE editor omit that tags automatically. So Here is the process to allow that:

In the dashboard you have the option to customize TinyMCE settings.

Go to Dashboard->System & Settings->Basics->Rich Text Editor

The url should be like (in V5.6.1.2): http://www.example.com/index.php/dashboard/system/basics/editor/

Here is the code sample that use can put into the editor while in custom mode.

print("// Schema is HTML5 instead of default HTML4
    schema: "html5",

    // End container block element when pressing enter inside an empty block
    end_container_on_empty_block: true,

    // HTML5 formats
    style_formats : [
            {title : 'h1', block : 'h1'},
            {title : 'h2', block : 'h2'},
            {title : 'h3', block : 'h3'},
            {title : 'h4', block : 'h4'},
            {title : 'h5', block : 'h5'},
            {title : 'h6', block : 'h6'},
            {title : 'p', block : 'p'},
            {title : 'div', block : 'div'},
            {title : 'pre', block : 'pre'},
            {title : 'section', block : 'section', wrapper: true, merge_siblings: false},
            {title : 'article', block : 'article', wrapper: true, merge_siblings: false},
            {title : 'blockquote', block : 'blockquote', wrapper: true},
            {title : 'hgroup', block : 'hgroup', wrapper: true},
            {title : 'aside', block : 'aside', wrapper: true},
            {title : 'figure', block : 'figure', wrapper: true}
    ]");