So, I'm loving the new spoiler formatting, it's very easy to use and fast to learn. A lot of my forum user use the non-limited >! version, which looks like this:
Peek-a-boo!
However, there is one problem with this approach - it create a "Details" object without a summary, and without a way to edit the summary.
First of, I'd like to stress why the summary class is necessary to have regardless of whether or not there is a default summary - without having this object, the browser defaults to its default. Now, the defaut depends on the user's language settings, and is in most if not all cases uneditable by CSS. This means that essentially you have very little control over the "Details" object itself. I've ran into the problem of wanting to change the default focus effect on it, but it doesn't get changed since CSS cannot access the browser default for some reason.
Second of all, it would be cool if we would allow our users to add a title to their spoiler. For an example, it could look like this (focus on the titled spoiler, not the graphics):

This is something we used to have on Xenforo, with the [spoiler="title here"][/spoiler] tags.
How would you implement this? Well, it's not that difficult, but you have to do 2 things:
- make the >! spoiler cover only text in the next line and below
- make the text in the same line as >! the spoiler title, or default to a translatable value (browser default "Details" is not translatable)
So, to achieve what I've taken a screenshot of after inspecting the element, you'd type:
>! Wonder what's below
mi branimo pravoslavlje
while without the title you'd want to type
>!
mi branimo pravoslavlje
Also, the feature is very clunky for multiline texts. This is a problem if you're trying to hide code blocks in a spoiler. So I'd suggest that instead of the >! prefix creating inline spoilers when closed by !<, you make the !< act like closing braces, defining the end of the spoiler block. The || can stay as the inline spoiler prefix and suffix.
Then you wouldn't need to do the following:
>! ```
>some line of code
>
>
> after a long break
>```
for this:
some line of code
after a long break
but instead just type
>!
```
some line of code
after a long break
```
<!