Newby Q on accessing html

Hello I am fiddeling around with the online demo. I see you can place a block to fill with plain vanilla html.
But can I access/ edit any plain html from within the editor?

E.g. If I code a template with an accordeon effect (like for a FAQ section) can the code be accessed from the editor so my client can add content?

Many thanks for your reply - Fred

Sure, no problem. You can always click the raw html section and edit again.