The following syntaxes work as expected (they create one spoiler tag).

The general rule here is that we allow 0-3 whitespaces before the starting colon, 3 or more colons, any number of optional whitespaces, and the "spoiler" keyword with any non-whitespace character after it.

Normal

    
::: spoiler spoiler
Hello!
:::

  

No whitespace

    
:::spoiler spoiler with no whitespace
Hello!
:::



  

Leading whitespace

    
   ::: spoiler title
Hello!
:::



  

::: spoiler title Hello! :::

Any number of whitespaces between : and "spoiler"

    
:::              spoiler title
Hello!
:::



  

::: spoiler title Hello! :::

Any number of whitespaces between "spoiler" and the first non-whitespace character

    
::: spoiler                 title
Hello!
:::



  

Three or more colons

    
::::::::::::::::::::::::              spoiler title
Hello!
::::::::::::::::::::::::



  

:::::::::::::::::::::::: spoiler title Hello! ::::::::::::::::::::::::

Here's where we run into some weird edge cases:

If there is an ending :::, Lemmy will consume the first instance of ::: only if ::: is on a new line with no other text (and up to 3 white spaces)

    
::: spoiler a
text (no whitespaces before :::)
:::

  

    
::: spoiler a
text (1 whitespaces before :::)
 :::

  

The following examples will show the ::: within the spoiler, and will make the spoilers nested

    
::: spoiler a
text (4 whitespaces before :::)
    :::

  

::: spoiler a text (4 whitespaces before :::) :::

    
::: spoiler a
text:::


  

::: spoiler a text:::

    
::: spoiler a
text :::


  

::: spoiler a text :::

    
::: spoiler a
text
a:::


  

::: spoiler a text a:::